Help......Sam's getting very agressive!!

Is Sam neutered himself? You may want to get that done before going to the park again. Dog parks are not for every dog.

Aside that - I would look into getting a full blood panel done, sudden, unprevoked aggression can be a sign on something more serious health wise. Was he hurt in the fight at the park? Pain can cause outburts of aggression too.

Sam's not neutered yet, we've lost his proof of rabies so he can't get neutered. As far as I know he wasn't hurt, the other dog has about half his size and it was broken up within seconds, I checked him for bites after words, there were none.

I can see in your profile that you have had Sam since he was a puppy and he is now 3 years.  I think you must know if this something totally out of his character..   so I would get him Vet checked.   If he has an ear infection, pain or hip soreness (or anything making him uncomfortable) he could get cranky with other dogs who want to play or ruff house.  I also saw he lived in a outside kennel, is he more socialized now?  Has he been at the dog park before?  happily?  with no incidents or is the dog park new to him?

A Vet check first and if all is well, you need to come up with an appropriate training program and start to desensitize and unstress him.  Good luck and keep us posted.

I asked my Mom what they were doing, and she told me she handed them each a rawhide. She told me Sam hid his and then went to take Taz's.

I guess Taz didn't want to give up his rawhide....but that really worries me because Taz is 18lbs and Sam is 53lbs. I can't have Taz being hurt...my parents would go crazy.

I'm woundering if it might be his age? He's 3, so he's coming out of his teen years....maybe it's his testosterone?

It very hard to feed dogs things they value together without supervision.   My dogs do fine with play toys but food of any kind can cause problems.  I always place dogs in different areas of the room and do not allow them to interfear in the other.  If they do I remove them or the yummy items.

This isn't aggression it more likely resource guarding.  Tell your mom not to do this when your not there to supervise there treats.

Where was his rabies done?  If you know, they will still have a record of it.  The way the tags work is that anyone can call the vet on the tag, with the number, and get a date on the rabies.  So they can certainly release that info to you as his current owner even if you don't have the tag.

If not, do as I do with a rescue with unknown history, and count it as cost of the neutering.  I'm getting two kitties spayed - 103 bucks each - and need their rabies also.  That will add a whopping $10 to each kitty's surgery.  Money very well spent for piece of mind - in this case, kittens that I'll never have to worry about going into heat, and when they start working outside in the barns, I won't have to worry about stray raccoons passing rabies to them, and then to us!

I also agree that a three year old is starting to make a move upwards in the social ladder and he may have a wee chip on his shoulder.  I'd keep him out of the dog park for now - that's no place for a dog that you can't show proof of vax anyway.

Good luck! 

He has the tag, but we've lost the papper work....and they won't take his tag as proof. We had it done at a local clinic, it was $10 for Sam and $5 for Taz. He's always played roughly and tryed to dominate Taz, but never so violent. I'm going to check all our files again, look for the paperwork.

If you have a tag - your local Animal Services will have the information you need.

Exactly, if you have the tag call the clinic you went to, they should be able to get you the records.  All of that is kept on file.

If you have had him since he was 4 months and now he is 3 years old he is due for his rabies.   My Vet gives my dogs Rabies sooner than 3 years because he there is a lot of it around my area.  Get him a shot and get him neutered, it is important to neutered him for many reasons

He got his shot around May of this year, and they told us that he wouldnt need one for 3 years....now I'm confused about that.....

Just.... go by the office where he had it done and ask them to print you another certificate. They have them, easily accessible. LOTS of people lose their rabies proofs. They're used to reprinting them. It's not a big deal.  

and if the clinic doesn't have one - go to Animal Control. They issue the tags - you cannot get a tag without a rabies vaccine - they'll have the proof their too.

Today Sam's acting totally different. He's acting submisive with Taz. Tail tucked between his legs, rolling on his back, not fighting back very much when Taz act's dominate.

I'm thinking he may have still been  hyped up on whatever he was hyped up on from the dog park.....