We also were having problems with the atv's accessing the property using the railroad tracks. I salted along the tracks with these below...and the problems soon stopped. I retrieved my units and have them saved for the future.
Cheaper than you think...I bought 15 boxes of them.
Caltrops Set of 10 Tire Spikes
Although I have an atv myself and use it a lot...I am not following the rules of proper atv ownership. Rule 1...Own less than an acre of land so you are forced to ride all over someone else's land. Rule 2...Think of only yourself while blasting around and tearing up the other's land. Rule 3...Litter belongs where you drop it. Try to throw your beer cans into the bushes instead of dropping them on the road. Rule 4...Assume you have a right to ride where ever you want.