Electric would be the cheapest option. We chose to use 4' high no-climb fencing (you can get this at Tractor Supply) and 1 strand of barb wire on top. Installed properly, they will no way pull it down. The barb wire is not really needed on top but makes us feel better about predators. The only bad thing about electric is if you lose power. I am also wary about heads getting stuck. We have had a head stuck in a gate and also a hay feeder.
