Spend more time in Cambodia. Making a three day tour to Preah Vihear from Siem Reap qualifies nicely. This World Heritage site has been contested between Thailand and Cambodia for a millennia. Fighting still breaks out making things edgy. We stayed in the small town at the base of the mountain in a clean but rustic inn. We ended up in the back of a 4x4 pickup truck for the trek up the hill. The road was under construction and would not be passable in our van. There was military presence everywhere, culminating in a full army base at the top. We were the only visitors. Incredible temple! Our guide was delightful and showed us into places we'd never discover on our own. The views from the top are spectacular. There are five gopuras leading you to the summit. Gopura 5 is an iconic image in Cambodian culture, seen on everything from t-shirts to currency. We spent 5 hours exploring. Thai army barracks and gunnery bunkers are in clear sight. A Thai highway comes to an abrupt halt in the middle of nowhere - the border. We never felt threatened or unsafe.
Postscript: This area did erupt into fighting shortly after our departure. People were killed, ruins ruined. Since our visit, the road is almost complete and they now charge $5USD entry fee, which includes a ride up the hill. Because of better roads, day tripping works if you tolerate driving 8 hours. Check with locals in Siem Reap who know the area. This is pretty tame, except for the guns and bullet holes. You only live once.