Electricity fixes that. Three wires about six inches apart. I use a 0.5J (1 mile) fence energizer on about 1500ft of fence. They test the fence often. I can tell because they make a very unique sound when they get shocked! However, even though they don’t have much of a physical barrier they won’t try to get out, even for food. It only takes a few days to fence train them also. 
Discussion
Appreciate that. I did have some poly wire inside the fence to sort of move them around this spring. It did work well. Unfortunately our setup is with woven wire as the perimeter. I haven’t had a ton of breakouts but if it continues I’ll probably run a wire along the bottom