Some steel, iron or.metal pipes buried in the ground. Cement them in as well as fill them with cement. Have them sticking out at least 3-4 feet, make sure you paint them, yellow or other noticeable color. UTVs are huge now so you can keep them about 2 1/2- 3 feet apart... post the property, purple paint on the trees and tell anyone you see its private. Get some game cameras up to catch those who skirt through....