I have a pony that has been dubbed 'too much horse' by both of the two people who came out to try her. Granted, one was ten and the other was 12, but I've had her since I was 12 and she's never been more than I can handle.
She has always been the type to plod along easily on a course without much input from the rider. She's also lived at the same farm all her life up until this year. January 1st she was moved to a barn where I noticed a change in her behavior for the worse. She was highly disrespectful on the ground - to the point that it was dangerous. Again, not too much for me, I handled her fine for the most part, but she became an issue for others. Still, she was perfect u/s. March 15th we moved to yet another stable. Here, she had an instant change in behavior, her respect returning and everything was normal. Nearing my final move, around early june, she started getting quick when I rode her. Her breaks were lacking and she was starting to get strong.
After moving to our permanent farm, she has become increasingly strong on courses. W/T/C she is fine, unless I do a lead change, then she gets a bit fired up, but it's still fairly easy to stop her. Trotting courses is fine, but cantering she can be difficult to bring back.
Some days are better than others.. Sometimes she acts like her old self, others she's a nightmare.
I've fixed it a few times, but she always seems to come back with the ickyness.
Here are some of my past posts about this problem: Just had to share my awesome ride :) Jumping out of the Arena :) Critique My Pony :) Is this a good way to deal with rushing?