The great thing about this bumper harness is that it's got 3 bolts on each side that attach to the harness. The harness should fit snug so it holds the bumper in place. I attached the video so you can see how great it works. You can see at the beginning of the video, I had to cling wrap the chairs and a coffee table - these are the things that the bumper can get past. It takes a little time for them to adjust but if you keep all furniture the same & don't leave shoes, boxes, etc on the ground, they learn the lay of the land. But, always keep the bumper on them to protect them. She wears it every day, all day unless I put her in a soft sided crate or an fenced area protected with soft sides, not har walls. I have a 6 lb min pin (they have bigger chests) and the XS is pretty close to the tightest fitting. I tuck the extra material back into the harness in case I need to use this on a little bigger pup at some point. Also, it loosens some with use, so I usually tighten clips up a bit every other day because you want a snug fit to hold bumper in place. Super fantastic product for our pets that need it. Awesome!!