Well obviously because they’re a bully who is my worst nightmare, they would most likely be running at me so I’d throw the lego strategically so they would step on it (requirement, they would have to be barefoot). Once they step on it (worst pain in the world rofl) and begin howling/falling down from pain, I’d quickly run at them and hit them on their head with a dog toy and wield my rock just in case they try to attack me.
If they begin to try to physically attack me (but at this point they’re pretty powerless due to the lego causing them to fall down and twist their leg) I’d drop the rock on their foot.
Done! And hopefully by then the doors would open. If not I’d use the rock to bash the door open.