Is it a genuine in front of the leg, forwardness though, or a 'horse wants to go fast' forwardness? Biiiiiiiiiiig difference and the latter is a frequent problem with a lot of riders of hot and ottb types, thinking the horse is going forward when it is just over reactive and running away.
The other cause can be unbalance, if the horse isn't in perfect balance and you try to bring it into collection, it can 4 beat. Again, sending the horse forward into an open hand will remedy this, with lots of work on balance.
Unless the horse has bad paces or their conformation dictates that they will naturally 4 beat, it is a forwardness/balance problem.
Do you recommend any balancing exercises? I do believe I don't help his balance at all....I just posted a thread in horse training about hand position....a dwarf riding an elephant!
When you say 'an open hand' do you mean just letting him stretch out and lope long? I'm assuming that's what you mean....
Forgot to mention, I've been working on loping long and picking him up with my legs and my hands for about five strides (it's almost always soft) and then releasing, and so forth.