Well hopefully he's not exercising too much until all that food has passed thru. I always fear bloat when dogs get into food.
If you live rural you may be able to find some cheap electric tape, same they use for horses and cattle and put it up at his height just inside your fence.
I have a top wire that is electric, suitable for cats and dogs because when we moved semi-rural our Gordon had sensory overload and was jumping the fence. At first we topped it up but then had to resort to the electric wire as it worked out a lot cheaper. I don't think it's been turned on for a couple of years now - they learn pretty quick. I've touched it accidentally gave me a good zap sure made me remember.
It's totally illegal here in NSW but you do what you've got to do to keep them safe.
The other alternative is to build a run.
He may need food dispensing toys to keep him occupied? At least he doesn't kill the chooks, my Gordon Setter was presenting me with the neighbours chooks, still alive (lovely soft gundog mouth) but certainly in shock and not impressed.