Barbed wire is okay to have, to long as it is properly secured and not hanging loose anywhere. Barbed wire CAN cause some major injuries, and can rub off a nice mane if the horse sticks his head through.
A good way to keep horses away from barbed is to put up electric band or wire. You can get solar powered, and battery powered chargers that last a surprisingly long time.
As for the cattle guard, is there anyway to fence off a section out of the trucks way and away from the oil rig at all? Thats the only solution I can think of.
Wait! I'll fix it....