www.arha.com has the different formats, rules, etc. for their trials.
Gundog Pack which is the division that I like is similar to SPO. It takes 2 wins and 150 points to Champion a dog in that format. Points are 50 for 1st, 40 for 2nd, etc. They look for a dog that runs pretty close to the line and works a check from the point of loss.
Gundog Brace is the same running style except the dogs are braced against each other instead of running them in a pack. Im not sure what the criteria is for Champion in that format.
Progressive Pack takes 2 wins if I remember right then you have to certify the dog which means it has to circle a rabbit on its own and be shot over to earn the title.
I dont have a clue about Little Pack or Large Pack trials.
In SPO it takes 3 wins and if I remember right 120 points. I think points are given for each dog entered in the trial so that if you win a trial with 30 dogs you get 30 points. There are lots of SPO guys on here that can straighten me out if Im wrong on that. SPO is alot harder to Champion a dog in imo.
I dont get to do it very often but I enjoy going to field trials. Itll never replace hunting for me but its a good reason to run dogs year round and it gives you something to do with your dogs when rabbit season is closed and you cant go huntin'.