That's what spurs are for.
You do have to have a very still leg before you can go in for spurs.
I use Prince of Wales spurs on my Gracie mare as a regular rule (she IS a slug on the flat - she gets nicely revved up when we jump.) I didn't wear my spurs out hunting because I thought she would be revved up like she is at a show (she is just perfect at shows). But after three hours of hunting she was lagging at the fences and I was PRAYING for those spurs! Next year, I'm buying a sandwich case so that I can carry a flask of port wine, my spurs, and a cell phone!