What I do currently:
I work him in a round pen without a lunge rope, he goes off my voice and body very well. I do use the whip, mainly as a guide for what direction I want him to go, or to flick it if he's being lazy and unresponsive. I don't hit him.
He will walk, trot and canter off my voice, and I'm trying to teach him to turn off my voice alone, although he will turn very nicely if I just use my body position, and he will come in to me when I ask.
Lately I have been putting a small jump in there just to mix things up so he doesn't get bored, and he seems to like that.
I lunge him mainly as an extension of groundwork, to teach him to listen to my voice and as a respect thing, but also to break things up and give him a little execise on the days I can't ride.
I lunge him, or try to at least, about once a week, never more, and only for about 20 mins.
Anyway, back to my question: what else/ what other exercises can I do with him to make it more interesting for us both? Or should I just continue what I'm doing?