ERECT whatever it takes to keep them out!
Grease up those bars on the fence so they cannot climb it!
Put sensors with LOUD BLASTING SIRENS THAT TRIGGERS FLASHING LIGHTS where we can!
Bury concertina wire under the fence!
We have a bazillion cars, RV's, semi's in the junkyards...dig a trench, stack those cars 4 high...build the fence on top! They need to be buried anyway!