This is best used with mo's creatures and downloaded as a save so you get the horses already there. There is 3 black horses 1 dark brown and 1 white flying horse. You ride the horse through the double doors and jump over the fence into a stall and since you can jump 2 squares high in a horse (and higher) and when you get off it can only jump 1 square high the stall keeps him from running around and the doors are for getting out of the stall when you have put your horse inside a stall.

Additional Notes

The floor is made of glass so other animals cant spawn inside the stall.
I added a schematic for those who just want the stable to get the horses you need to add mo's creatures mod to minecraft and get the save.