I used to use a hanging tennis ball, but for the new house we went out and bought this for the admirals car.
Laser Parking Assist She pulls her car in, and watches that laser flashing on her hood, and stops once it hits a predetermined spot on her dashboard. Perfect park, every time.
I have to back my Durango in to make it fit, and make sure I can open my door to get out. I back it in until my passenger side mirror is back to a certain point on a garage cabinet, then I stop. If I go a few inches to far, my trailer hitch receiver would go through the wall. Hasn't happened yet!