Max is close to 100 lbs and the chihuahuas are 2.5 and 3.5 lbs.

Max is surprisingly careful around them. He was actually terrified of them at first! But - I won't let them run around together. If Max saw a squirrel and started chasing after it, he might step on one of the chis. Indoors, if somebody knocked on the door, all 3 dogs would go nuts and somebody would probably end up getting stepped on.