Help! Flying Lead Change

So my OTTB is a big lug sometimes but I of course love him. He canters great a little to far in from the rail sometimes but we are working on that, I think that it is due to his LARGE fear of deer. Even though they can walk under him.

What the real problem is no matter what I do or how many signals I give him he just wont ever do a flying lead change. We circle and loop around the ring for what seems like forever and he just wont do it. He will slow down change leads and continue on, but never on the fly. We have been training for shows and I do not want this to become a problem in the ring.

Any suggestions?

You have a video of you for I am pretty sure what is going wrong.

As Spyder requested, a video would be great. My bet is that he's 1. Not ready for flying changes 2. You're not setting him up for success in order to get the change 3. You don't have experience in changes yourself.... list is endless. Video would be great. I'm interested to see how you have him travelling in trot and canter. If your canter is not established and the horse is on the forehand, or you don't have an established half halt, you're going to run into problems in the changes.

I'm still learning in this aspect... But maybe he's not balanced enough to feel confident performing a flying lead change?

-Because I know that my horse isn't cantering well enough to do flying changes yet... But in saying that he is only new with me and I haven't worked with him much (Injuries)

I don't have a video but I can try to get one and post it for you guys. I don't think that experience is a factor I have been riding for well over ten years and he is 17 and way past his green years. I did just get him a month ago so we are obviously still working out all of the kniks. Ill work on that video today when I am riding. Thanks guys!

If you have some pictures that can help so we can see how you ride and how you organize yourself when you are in the saddle.

I can definitely get pictures today! But I will try for the video and pictures for optimal critique