Really easy fix if your door knobs are round. If they are lever style, of course this won't work. People can open them, dogs can't. You can also put a safety latch on any cupboards with dangerous chemicals and on the fridge. Use regular childproofing methods to keep things closed and this will greatly cut down on his ability to open door, etc. You can find a vast array of door knob covers, safety latches, and other items to prevent him from doing this.