We had a gate we tried to use to keep the cats from going into the basement. Yeah right. It was 4' tall, and they were still Kittens. They just jumped up, and scrabbled over it, and down the stairs they went bumpity bump. Moved the gate, and they were able to walk down the stairs. At that time the doggers were either outside, or in the garage. Not certain, but being as they weren't the smartest doggers in the world, I would surmise if they saw the cats jumping the gate, they would too. So I think a cat sized access hole, or widened picket would be best, unless it was a smallish dog. Seems like if you forbade them from going somewhere they wanted to check out, then they got criminal about getting there, no matter the obstacle you tried to impede them with. Like they accepted the challenge. :-)