For nearly four decades, the Assad regime in Syria ensured that the border with the Israeli-controlled Golan Heights remained quiet. But in a treeless valley at the foot of snow-capped Mount Hermon, it's clear that is changing.

"Things can change dramatically in hours," says Kobi Marom, a resident of the Golan Heights ski village, Neve Ativ, and reserve Army colonel, as he surveys the valley. "We are trying to be prepared for a new situation in the region."A sturdy new fence, surveillance sensors, and troop deployments along the Israeli side of the 65-mile border reflect concern in the Jewish state about the spillover from Syria’s civil war and what comes after the expected downfall of Syrian President Bashar al-Assad. Errant fire from Syria has already crossed into Israeli territory several times, prompting Israel to fire back once.

After two years of watching the Syrian conflict from the sidelines, the hostilities seem to have arrived at Israel’s doorstep. Syrian rebels are fighting to wrest control of the border from the Syrian Army, and there’s an increasing fear that militant groups on both sides of the civil war will get their hands on the country's advanced weapons arsenal and set their sites on Israel next. That presents a quandry for Israeli officials: Can they protect the country without getting sucked in to Syria's violence?

Treading a very thin line

Analysts say that balancing between the two will be increasingly difficult if the central authority continues to crumble in Syria and multiple power centers emerge in the countrywide war.

But some Israeli officials and security analysts see an upside to the chaos. The fall of Mr. Assad could be a strategic boost for Israel because it would sever the "Shiite crescent" that stretches from Iran to Lebanon, connecting Hezbollah to its supporters in Tehran. And former chief of IDF intelligence Amos Yadlin recently said that Israel has become more secure because the Syrian Army no longer poses a conventional threat to Israel.

"The main question is the day after," says Bernadetta Berti, a fellow at Tel Aviv University’s Institute for National Security Studies. "From the Israeli perspective, a Syria not ruled by Assad is something that it should look upon favorably, but from my perspective the day after, Assad will be complicated."

On one front, Israel fears that rising chaos and the proliferation of Islamist militants just beyond the Golan Heights fence could lead to cross-border attacks like those from Egypt’s Sinai Peninsulainto southern Israel after the fall of former Egyptian leader Hosni Mubarak. Israeli communities in the Golan Heights have already been put on alert, and local Army commanders said they have formulated a new defense doctrine to cope with the Syrian instability.

Israel also worries about the transfer of advanced weapons and chemical warheads from Syria to the Lebanese militant group Hezbollah, a development Israeli leaders consider a "red line" because it could give the Iranian ally a major boost in a future war. In late January, Israeli airplanes reportedly bombed a convoy in Syria carrying anti-aircraft missiles to Lebanon – the first major Israeli attack on Syria since 2007.

Even though Israel never officially claimed responsibility, Defense Minister Ehud Barak said after the attack that Israel is serious about blocking the transfer of sophisticated weapons from Syria to Lebanon.

One Israeli Middle East analyst cautions that Israel risks becoming embroiled in the Syrian fighting, much like Israel became embroiled in the Lebanon civil war, culminating with an invasion in 1982.

"If you draw a red line, you will have to enforce that red line, and that will push you into the conflict," says Guy Bechor, a Middle East historian at the Herzliya Interdisciplinary Center. "We have been there in Lebanon trapped in between religions and sects. This is not our war."

A 'developing threat'

Back on the ground along the Golan border, Israeli soldiers and civilians can observe and hear the fighting less than a mile away.

A week ago, Israel accepted for the first time a small group of wounded Syrian rebel fighters who requested treatment, raising questions about whether Israel would become a shelter like other Syrian neighbors.

Israeli Prime Minister Benjamin Netanyahu, who is pushing to complete construction of the Golan border fence, said afterward that as a rule Israel will not allow Syrians to cross into Israeli-controlled territory, but would make exceptions on "humanitarian grounds."  

Senior Israel Defense Force (IDF) officers in the Northern Command began predicting last year that, amid Assad’s collapse, the Golan might be targeted by militants backed by Iran or global jihadist groups who have flocked to Syria to join the fight against the Assad regime. The IDF declined to comment on the border situation this week, but Mr. Marom said reservists have been replaced by regular elite forces recently. Two months ago, a senior officer said the IDF had updated its intelligence gathering effort, and adopted a new operational doctrine.  

"The combination of all of this is to meet the developing threat," said Brig. Gen. Tamir Heiman in a December interview with Channel 2 news. "I don’t know if it will happen, but it’s good to be ready."

In the Alonei Habashan farming cooperative, located just a quarter of a mile from the border, residents are also ready.  The main gate is closed at night and residents say they are locking their doors for the first time for fear of infiltration. "We will get hit first," says Yiska Dekel, chairwoman of the local board.

Now that the Syrian regime is fighting rebel forces right on the border, the Army considers the border region an eyzor sfar – a "frontier region" – with a vacuum of authority, like Egypt’s Sinai Peninsula. In the absence of a central "address" to retaliate against, the question for the Army becomes how to respond to infiltrations or the possibility of rocket strikes from Syria into Israel.

Military officers have spoken of retaliatory incursions. Another defensive solution would be to enforce a no-man’s zone by shooting into a defined area along the Syrian side while staying on the Israeli side of the border – a tactic used by Israel in the Gaza Strip in recent years.

Israeli analysts believe the best-case scenario for a post-Assad Syria would be a Sunni-dominated government with ties to Turkey and the Gulf. However, that may be a long way off, and in the interim, further chaos is likely. Reserve Colonel Marom predicts that the power vacuum will continue over the next two to three years. If attacks on Israel escalate, Israel may find itself mulling the establishment of a security zone inside Syria – just as it did in southern Lebanon before withdrawing 2,000. That would entail a limited ground invasion

"I hope the Army has a plan for a security zone," says a security officer at a Golan Heights Israeli community who declined to give his name because he is subject to the Army. "I don’t like it, but if no one gets control over Syria, we’ll have no alternative."