At least 28 people have been killed in outbreaks of violence since 2011 over the ownership of a patch of border land next to the 900-year-old Preah Vihear temple.
The Hague-based International Court of Justice (ICJ) is due to rule today on the territorial dispute, but there are fears the decision will revive nationalist tensions and spark renewed clashes.
Tens of thousands of people were displaced in the fighting, leading Cambodia to ask the ICJ for an interpretation of an original 1962 ruling.
Leaders of the two countries have appealed for calm before the ruling by 17 international judges.
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The mood on both sides of Preah Vihear temple was tense early Monday, with tourists still allowed to visit the ancient structure via Cambodian territory. But journalists were denied access.
Local residents on both sides said they were taking no chances.
"We have already prepared our bunkers in case Thai troops open fire," So Phany, a vendor near Preah Vihear temple, told AFP.
"We have to take proactive measures. I will leave my home for a few days, we fear that Thai troops might cause clashes," villager Va Vy, 29, told AFP as he prepared to leave.
The Cambodian army denied local media reports that it had sent military reinforcements to the area.
"The situation along the border is normal," regional military commander, General Srey Doek, told AFP.
On the Thai side, some 40 primary schools were closed in one district on the border Monday, according to a provincial education official, Somsak Chobthamdee.
On her Facebook page Thai Prime Minister Yingluck Shinawatra vowed Sunday to "consult" with Cambodia after the decision to avoid any conflict, adding her government would make a statement following the verdict.