<< Rather than just pulling on the reins as a brake, remember to sit
 deeeeep
 in the saddle. When the horse starts revving up, and you pull on the
 reins,
 there is a tendency to hunch up and get your weight out of the saddle. I
 had 
 this bad habit of this for a while and realised I was egging the horse
 on, rather than sitting deep and telling him to sloooow. Theoretically 
 (and I say theoretically, because on a revvy, naughty horse it probably
 doesn't work) you should be able to stop your horse purely by sitting 
 deep - no reins necessary. >>
Dear Lucy--thanks for adding this--you are entirely correct!  I try to sit
deep as well with David.  Don't always manage--like when he's acting as if he
REALLY wants to buck up the upcoming hill>g<--but I do try and tell myself to
relax, breath deep, sit deep, keep soft hands---it helps--A LOT--
I have my friend Sue trained to tell me when I look as if I am "tightening
up" while David is acting nervous--it is a nice reminder sometimes. 
Trish & "pretty David" (who was a very good boy today--we're gonna become a
real team yet--)