While I have done some butt sliding trail riding, I stopped being able to jump on my horse before I was 25.
I don't own a horse that hasn't wished for a bag over their head when I have put them in some stupid "predicament" just so I can get back on:)
I look for anything to get back on:
1. A hillside to where I can get a little above the horse.
2. Big rocks.
3. Big tree limbs.
4. Stand the horse in a deep ditch.
If the horse won't stand still -- school them at home to learn to sidle up next to anything and everything. My philosophy is "I have until midnight, it's your choice." Annnnd I have two horse that found out I meant that - lol lol
Lastly, never-ever get off the horse until you've found something to put the horse beside or down in - lollol