I should of used the term "cage frustration" instead of aggression. He pulled the same thing on me the first time I saw him at animal control. He was growling and carrying on but his tail was going a mile a minute so I walked into the pen with him and got GSD kisses.

He was just frustrated with being penned up and abandoned and he was letting me know about it. I would just take him out of the crate and put him in a sit and scratch his ears. After he relaxed I gave him the Kong and put him back into the crate. Then ignored him but stayed where he could see me.

He now knows I'm coming back and he's stopped doing it all together.