Dog’s actually like be anally penetrated as long as their slowly trained from a puppy. Obviously big dogs take it better then small dogs. Rottweilers are my favourite coz they short haired and they don’t have tails. Doberman pinscher would be my second choice but they generally to tall to do d********** with on a flat surface like a bedroom floor. Excuse the “d**********” pun. German shepherd is ok but I hate fluffy type dogs. As for their pooholes all 3 feel equal with perhaps a slight edge to the Doberman. I always use an oil based lubricant and always have a thick towel underneath coz they love to fart your sperm out all over the floor/bed/sofa.