I have a 4yr old that has been sitting for some time, in the round pen he really keeps his head up high, not collected at all and flys around. Can anyone reccommend a lunging aid I could order like with a surcingle? I saw there's an EquiAmi, but for $200 that seems pricey for just a few ropes? Thoughts/suggestions to get him to use his butt and collect while I lunge? Thank you

Firstly, what is your GOAL with lunging the horse?

If you want to get him in shape .... why not ride him? Sure, you can stick some sort of contraption on him to force his head into a false posture (which will not be true collection). Or you can ride him with your seat and legs and teach him how to do it.

Personally, I don't see the point of lunging endless circles. Those circles are hard on their bodies, and I don't find it does much good of anything. I don't mind doing ground work in the round pen, but that consistents of lots of direction changes, gait changes, stops, rollbacks, etc, and lots of LISTENING that the horse is doing. (not just going around in circles)

My two cents, anyway.

Instead, teach him not to fly around. Teach him to listen to your commands and be a more attentive, respectful horse. This is benefit the riding as well.