:hug: I would put the fence up. He will ultimately learn how to climb under it/through it like we did on the farm, but it will stop him.
Also, I would get some slide bolts for the doors - put them up the top of the door so they ram home to the top of the door jamb.
He won't be able to reach them, even from a chair.
The other thing I am sure you are already doing it talking with him about the dangers of running off - he is old enough now to grasp some of the really basic concepts about hurting himself, losing mummy etc. Keep reinforcing that point, esp now you are UTD - things will only get harder to chase after.
:hug: Put the fence up. It is not child abuse, it is simply what will work, keep him safe, and you sane. He will not hurt himself, and no, he is not a cow, but even children need to learn the hard way sometimes.