Simple answer is a fence, you can always have a gate in it. For short term put in some wooden stakes with caution tape on it at the point they are entering the field from your driveway/property, blocking the route (at the point you would put the fence). You need a marked barrier even if it is not truck proof they will get the message and all but the biggest jerks will go else where or take another route, tape and stakes are cheap. Fence is the long term solution, or maybe posts with a chain etc.
As for them using the field, no one but the owner has domain over the field... You may be able to call the police and complain about dangerous use of a motor vehicle in the field they may come and hand out some bogus tickets, big grey area may....