I don't have a dog right now, but I used to have a few. I had a large pit bull one time, and I took him to the bathroom, but I was too scared to all the way so I thought I would try anal instead.
Huge mistake. No preparation, he just took over and ended up locking inside. I never felt so much pain, like I was sweating. I couldn't get it out and it was pushing the walls or something. I was worried someone would find me like that. I was sitting there struggling for what felt like an eternity until he finally was able to be pushed out.
I never did anything again after that.