Have you thought about an invisible fence? We have two big dogs we keep close with one. The systems vary in price, depends on how fancy you want to get. We just got one with a little box, the wire you bury and two electric collars. We were able to "fence" in about 2 acres and it gives them plenty of room to run but keeps them out of trouble and on our property. It took very little time to train them that when the collar beeps, you stop. Neither has been shocked in a long, long time. You just have to make sure you don't let the batteries go dead, some how they always figure it out.
This works for most dogs, not all. Our rottie and shepard mix respect the collar, but our scottie will run right thru the area that the collar will shock him. We even put the stubborn dog collar on him and he STILL would take off. Who'd of thunk such a little dog could handle that kind of shock. Especially when the big dogs won't even push the boundaries?
The hardest part of a system like this is burying the wire. That can take a little time, depending on the size of the area.