Things he does....He lunges perfectly both free and on lead all by voice commands. He backs up by voice commands. I'm teaching him neck reining which I'm a little rusty on that (I'm using the crossover rein method). Any suggestions? I would like him to turn very easily once the rein touches his neck - not sure how to do that.
There was a very good step-by-step article in Horse Illustrated this month on how to teach neck reining. You might want to check it out. They do an excellent job of breaking it down and explain it much better than I ever could.
Some things I would like to improve but can't remember how - I would like him to round his back and neck, I keep leg on him but he doesn't respect the bit yet - I'm using a snaffle with a shank, should I go to a slight curb bit? Any suggestions?
I would suggest switching back to a regular snaffle until you get him responsive to all your cues. The mouth piece is not what classifies a bit as a snaffle or curb. You can have a snaffle with a solid mouth piece and curb with a jointed one (like what you're using now). Technically, any bit with shanks is considered a curb bit. As far as getting him to collect, it's great that you are using your seat to drive him forward into the bit. Lynn Palm wrote an excellent book on this subject called The Rider's Guide to Real Collection. You might be able to check it out at your local library. It has a variety of good exercises you can do with your horse to help build a balanced, collected frame.
Any other ideas on what I could teach him? Its winter so our only option is the arena.
A couple of other things you might want to work on: pivots, turns on the forehand and side passes. These are great buttons to have on your horse! Plus, being able to control each part of your horse's body will really come in handy when you're ready to move on to more advanced maneuvers down the road. Just be sure to take it slow and train each side individually. I've also found it helps tremendously to start teaching the cue from the ground before moving into the saddle.
I hope that helps. If you'd like for me to go into more detail on some of these thinks let me know. I'll do my best to explain them further.