It may be expensive but maybe he ought to think about putting up a high voltage electric fence where they are coming in. If afraid the cattle might be harmed then put the electric fence on the outside of his normal fencing. Put up signs with different languages, trespassers will be shot on site. Oh what about a motion detector that goes off with either a loud sound or the sound of rapid gun fire? Might make some think twice. And every once in awhile him & some other ranchers can sit out there in the dark with guns, and shoot when they hear the illegals coming. Even better if the ranchers had night vision goggles ?