Great post MyBoyPuck!
I have the worst trouble keeping my legs at my boy's girth when going over a jump! It doesn't matter the height of the jump, because he over jumps a 6inch crossrail like its a 2foot oxer. I'm still working on improving my timing and not jumping before he does, but I feel like my legs fly back when he is landing. Would it improve with my timing? Do I need to do leg exercises? How can I fix this?
It would help if I could see pictures, or a video.
The biggest reason why riders loose their lower legs over fences, is because they pinch with their knee's.
You have to remember, that one of the most important factors to being solid in our tack, are our heels - without our heels doing their job, we have no anchor. No anchor = no solidity in our tack.
So, we must learn to allow our bodies natural weight flow, go from our heads, into our seats, and from there, into our heels. But, the moment we pinch our knees, our weight flow has no where to go, when it is blocked, it cannot continue on downwards - so we lose our lower leg.
When we open our knee's, and allow that weight to dispurse past our knee's, and sink into our heels, now we have that aid, that anchor to help us remain solid.
I like this quote from George Morris, because it makes me rethink my leg position. "We must be wrapped around our horses, not just be ontop". I like this because it re-emphasises how important it is for us to train our leg muscles as to where they need to be, but also helps us to remember that we are asking our horses to come up into our seats, even when over the fences.
When you are wrapped around your horse, your legs will be "glued".
So, heels taking bodies weight, legs glued to your horses side, and knee's opened.
I need to get my lower leg back to where it needs to be. I used to have very solid legs, until I stopped working on keeping my muscles trained. I used to spend hours hacking, while up in 2 point position, with my legs wrapped around my horses girth.
Next, take your half seat out for a spin. Walk/trot/canter around in it with the goal of not changing a thing. If you stay in the proper position, you should not have to grab mane to hold the position. If you fall forward or back, go back to step one to re-establish where your lower leg should be. It might take a bit to reset your muscle memory, but it'll come. Practice this step until your lower legs are absolutely glued to your horse's side.
Just to add to this - I like to call it a "Functional Two Point Position" - the most important factor here, is to get your legs under you. As my coach says "Balance over your feet". Remember what I stated about opening your knee's and allowing your bodies weight to flow into your heels, and have your legs wrapped around your horse.
Every upstride, your legs are saying to your horse "hey, come up to me".
Get your seat bone tucked under you slightly, where your lower back is strait, and activate your core. Your core is very important! Without your core, you are just a limp noodle ontop of your horse, not being very helpful at all *remember, team effort*. Chest open, tall upper body and make it feel like you are lifting your heart.
Balance over your feet.
Hope that helps