Great advice from Karen!
Another thought for you to throw into the mix:
Both my horses love to jambette as well. It's especially my girl Circe's default move -- when in doubt, get that leg up in the air and wave it like a conductor!
Especially when she first learned it, she was obsessed! (I actually have yet to see a horse who doesn't love it once they get the hang of it...)
We've tried a variety of things to control it (along the lines of what Karen has suggested) and they made a difference, but she still was doing it fairly frequently.
But -- I recently realized that she would do this when she was uncertain or lacking confidence. If I asked her something that she didn't understand or wasn't sure she felt okay about, she'd pop up that leg. This shifted my perception of it from being something that I was tired of her doing to feeling like it was an opening into her saying, "help, wait, I'm not sure about this thing you want!," which actually suddenly felt really helpful because it became a cue for me to step back, slow down, and think about what might be bothering her and how to fix it.
So, now, when she offers the jambette, I reward her with a treat and a big rush of soft, happy, 'aren't we both wonderful' energy -- we both benefit from that. It's become our tool to recalibrate. We both get a big dose of relaxed and happy success and I find that she's then almost always willing to try what I've asked for next.
May or may not be relevant for you and Er, but it's been a powerful enough realization for Circe and me that I thought I'd share!
All the best,
PS: Please, don't have any worries about posting in the 'wrong' place -- it takes a little while to figure out where everything is, here, especially as the forum has gotten bigger. Romy is our resident human encyclopedia and helps us keep things organized!
"Ours is the portal of hope. Come as you are." -- Rumi www.imaginalinstitute.com