I'd install some sharp metal spikes along the boundary & post a warning sign
B E W A R E!
Stihl Kombi System
028 Super, 066 Chainsaws, PP 800 Pole Saw
F-150, F-350 Trucks
Ariens Rear Tine Tiller
5x12, 6x12, 6x14, 8x16, 7x18, 6x22
Asus Transformer Infinity TY700 Tablet
If you think it's expensive to hire a professional to do the job, wait until you hire an amateur.