If possible, make a simple addon that has a think geolod, that's it. Put it over the fence.. you'll smack into geolod, not the fence
If that's not possible, hmm.. a trigger over the fence, and aboiut a meter either way, grouped to the cars, if any of htem get within that trigger, it gets setvelcity [0,0,0], so it'll stop isntaltly
- Ben