Will doing groundwork help him behave better in general?
He is amazing in hand. Doesn't cause any problems. He can be right next to a mare and if I see him even look at her all I have to do is say his name and he will look back to me. He respects space, doesn't try to run you over or pull you or anything. If he has a halter on or even a rope around his neck then he knows it is time to work and not act like a dingus. Of course he is still hot under saddle, but that is just his personality. On the ground he is great.
Put him in a round pen and you can just stand beside him, with no lead rope. If you walk, he walks. If you jog, he trots. If you stop, he stops. If you turn, he turns...etc. In that matter he is well behaved. He is just irritating with other horses when I am not there. I never actually get to witness the behavior I am telling you all about, I just hear about it from the barn owner.
I found teaching Brock some more difficult liberty stuff really helped settle him down and he stopped being so fixed on his neighbours, whether I was there or not. I teach him new stuff under saddle too, but there are less limitations ability-wise and fitness-wise on the ground so the liberty work really does have value. He still will show interest in a mare in heat but jeez, they're flipping their tails and pressing their butts toward him and peeing everywhere - poor boy can't escape the female attention! They all seem to think he's the horse equivalent of Tom Cruise (only taller of course! ).