Moose keeps getting out of his harness and its a huge pain. We cant get a smaller size because it's…

Moose keeps getting out of his harness and its a huge pain. We cant get a smaller size because it's too small and it hurts him. He snaps actual collars like its nothing. He has one on with his tags on it but he can bust it off without even trying. When my SO isint home i have to put him out on the lead for him to go potty and I normally stand in the window and watch him so the kids aren't in the house alone. (He can take 20 min or so to actually go potty) Today I let him out and AJ needed to go potty so we ran into the bathroom and I come back out and there sits the lead and his harness and no dog. I ran and grabbed AJ and we started looking. In our jammies for the whole neighborhood to see. Couldnt find him and I went back to the house to grab AJs stroller and there he sits on the front porch. Gave me a damn heart attack. I need to get him chipped instead of just the tag incase he were to somehow get his collar off or if someone were to find him and try to take him. We are looking at places and one of the top things on my list is a fenced in back yard. But for now i need to figure something out. Hes the sweetest dog in the world and wouldn't hurt a fly but seeing a 75 pound dog running at you is scary especially if you don't know the dog. And theres a ton of pitbulls in our neighborhood and not all of them are friendly with other dogs. I cant wait to move somewhere we can just let him run free. Idk how far he went before coming home and idk if he were to go farther than our little circle if he could find his way back.