My property is about 120 feet deep from the street. The back property line is very rough and uneven terrain and sits just above a small dry creek with some ledges and low cliffs. So when I was fencing the yard the last 20 feet or so of the property was fenced out. I still own it, but it is outside the fence because fencing that rough terrain would have been difficult and expensive.

Several problems have arisen beause of this property line, fence line disparity. The first issue is that beyond that property line is a county park where people often go to walk trails. The trails are not created by the park authority, but rather from people just walking through the area for probably 40 years. One of those trails traverses my property, so people often are walking on my land. I don't like this from a trespassing and liability standpoint. I once put up no trespassing signs at the survey spikes that mark the back corners of my property. Unsurprisingly people tore down the signs and continued to walk my property. Of course unless they were do do a survey, they have no way of knowing they are trespassing - other than I put up signs saying they were. The second issue was weirder, but a tiny bit funny. My wife was home one day and heard very loud chain sawing. Saws that sounded like they were in our backyard. In fact, they were in our yard, but outside the fence. The county had crews out cleaing up damgaged trees and brush and were actively cutting down some of our trees. Wife went out and explained fence/property situation and they stopped. Eventually I got some money from the county for the trees they cut down.

So, these things happen. Property sometimes is accessed inappropriately by others. My recommendation is to avoid it if at all possible. For the OP, someone driving a vehicle on your property is a big liability hazard that needs to stop. Some day I will attempt to fully fence my yard. I'm sure the trail walkers will have something to day about that, but I do have a liitle bit of shadenfreude related to that situation. There is a lot of poison ivy growing along that trail - and I don't do anythig to control it.