It is very important to make sure the bridle fits well enough that it cannot be rubbed off. With your guy's rock star mane, keep the bridle path trimmed. A lot of people are now using a strap of leather that goes from the throat latch to the nose band that keeps the bridle on, just a bit of added security. Also a full nose band is important to keep the bridle properly adjusted.
Gullet Strap | Iowa Valley Carriage
You can use any strap of material to make this to start.
The number one rule in driving:
Never take the bridle off while the horse is hitched to the vehicle.
Infraction of this rule can get you eliminated from competition and/or asked to leave the premises.
Does your pony know how to drive yet?