Why do riders resort to using gadgets and false aids/hands when trying to obtain control?
When you want your horse to come back down to you, use your proper aids, just as Strange stated - Your CORE, thighs and upper body. Same aids you use, in the dressage ring when doing a downward transition.
Lookit - you give a horse something to lean into, they'll take it. #1 rule I have learnt when riding in Eventing Clinics taught by Upper Level Riders is, don't fight, dont' argue.
I highly suggest you start establishing your Coffin Canter, obtaining a functional two point position *USE YOUR BODY* to get your horse to come back under you. Very important aspect to have while you are out there.....you need to know how to rock your horse back under you.