Raccoons can lift and push a lot of weight. I was using a 50 lb boulder to secure my chicken shed when something broke the latch off (probably a raccoon or human, both have tried to break in). It worked for a two years but then the raccoons managed to move it and a chicken massacre ensued. I knew it was raccoons based on the claw marks they left and the method of dispatching hens. You would think it is easy to push the boulder but it takes a lot of effort to do so.
We still don't have a new latch and right now I use a large drawer, probably about 80 lbs to keep the coop shut, along with a heavy shovel, and some plastic sheet to cover gaps at the bottom of the shed door, and the same boulder is placed inside the drawer. There is also a large branch that rests upon the door. I hate this set-up, it takes three minutes to lock them in and get them out, so we'll repair the door soon enough. But raccoons are strong. I don't want to risk losing any chickens at all.
https://www.aphis.usda.gov/wildlife_damage/nwrc/publications/17pubs/REP 2017-031.pdf
This paper entails the strength testing of wild raccoons. Raccoons will generally not lift anything above 30 pounds, anything below is fair game, but based on my experience I would still opt for something heavier