Thank you all for your replies. I have an update I would like to share. First, what didn't work, last Wednesday, he continued to be very aggressive in his cage upon entering (i.e. he would spin around and viciously attack the cage door/opening). All while wagging his tail, which signaled to me he was being dominant aggressive, I could be wrong but that is what I thought. So I tried the dominant dog collar and lifting his front feet off the ground until he lost his air, big mistake! As he began to lose his air he climbed up the leash and latched on to my hand, eventually I removed my hand from his mouth and he was incapacitated (lost his air). But this did not solve my problem. He was still was aggressive upon entering his cage. I am not saying that hanging a dog doesn't work, but it may not work on all dogs.

What did work, I had him enter his cage, he turned around and did his usual aggressive, I want to rip your head off display and in a calm assertive tone I told him to platz. When he eventually did, and was calm and not aggressive I rewarded his behavior with a treat. Over the last several days I have continued this tactic and he is no longer aggressive upon entering his cage.

In addition, I have removed all of his toys and really focused on being his leader and not his friend.

Jack - you are 100% correct - using prong collars or dominat dog collars are not always the solution. Crate aggression is a perfect example of this.

Sometimes sitting back and really thinking about the problem will give you ideas on other approaches.

I would like to read (learn) more about "crate aggression". What is it, what causes it, and is it a problem that is well understood in dog psychology?