Question: When my 18 yr. old foxtrotter canters on her left lead, she canters in the front and trots behind. On her right lead, she does a regular canter, but it is faster than when she is on her left lead. What can I do to get a good canter on her left lead? Is it that she is just 
going too slow and if I speed her up she will perform a regular canter? Is it pilot error?

On a horse this age, you may be getting a touch of arthritis in back, hocks the usual place...not to worry, the work, if done slowly and gradually to build her up at first, will actually be beneficial, especially if done on a regular basis.

From what she's doing, it may be from not being cantered very much, or previous lack of complete training on the canter, or some of both,too. Work large circles, both directions, to help strengthen both sides. Most inexperienced horses (inexperienced with actual training for the canter) will do either of the things you describe, even young ones. An older horse not worked for a period of time in a particular gait may "remember," but lack of use creates out-of-condition musculature, so even if the brain gets and gives "the message," the performance will not be to par until some conditioning is done.

One the right side, initially work at the speed she can handle it; a little faster is normal, and the circle should help slow her down somewhat, and continued regular work...start short periods, larger circles, then gradually lengthen time, decrease circles every few days...ask as you feel her better physically in condition to handle it,so that her body is up to part to 
perform as her brain tells it to(after getting the message from you). On the left, you may have to speed her up enough to engage the rear; dont worry about controlling speed yet, get the correct gait first, then work from there as on the right. Do be careful that your hands and body position are helping, and not hindering. Unlike gaiting where the balance/weightbearing stays quite stable and in the rear/back legs, in cantering, the weight 
shifts from back to front(inside lead leg), and the head plays an important roll (being the fulcrum of balance), so be sure you're helping with your body and hands, not inhibiting it...helping push with your seat at the appropriate rhythmn does help.

Your horse's situation rather reminds me of when I sat down to a piano after many years of not playing, whereas I was quite accomplished at one point...I was SO frustrated not to be able to play any better than a beginner! I could read all the notes, knew just where the keys were, but my hands just couldn't do what my brain told them to...it took a couple weeks of practice to get back to the point I'd left off! (rusty!)So take your time in working with her, while she "relearns"...she's likely just as frustrated as you are...after all, for a horse, the greatest joy is the accomplishment and agility of movement.
 
Stella

Hi,
First I would rule out a possibly sour back or hip. Sometime it can be something as simply being out of alignment. Also check if your saddle fit is ok. A pressure point in the wrong place could also cause this problem.

If all is ok then maybe start doing some lateral exercises such as shoulders in and shoulders out. It is normal for a horse just like people to be stronger on one side and weaker on the other. Build up the muscles and working towards more flexibility on the weak side can
help this a lot. Also yes check to see if your horse is better at a bit more speed and ask for collection and a slower speed slowly. If the your horse starts to break into the undesired place speed back up again till the canter is again three good beats and then re-ask for it
at a slower speed. 

Good luck
Liz