Respect What a Mustang Is Built to Do
A Mustang's first answer to a threat is distance: run early, run far, decide later. That instinct kept wild horses alive, and it does not switch off because a horse now lives behind your fence. Fireworks deliver exactly the stimulus that triggers it — concussive bangs with flashes, arriving from no direction the horse can identify — so your whole plan should assume the horse may run, and make running survivable rather than trying to prevent movement altogether.
Choose the pen with the soundest fence, no wire he can become tangled in at ground level, and nothing stored inside it that he could strike at speed.
Fencing Is the Whole Ballgame
Walk the perimeter in daylight and look at it as a frightened horse will meet it: at pace, in the dark, possibly shoulder-first. Replace or brace any rotten post, tension loose wire, and check that panels are pinned so they cannot lift. Corners matter — a horse running a fence line funnels into corners, so clear debris and stored equipment out of them, and consider whether a rounded or blocked-off corner is possible for the night.
Gates deserve their own inspection. Chain and latch every gate, then add a second fastening, because a Mustang leaning or striking in panic tests hardware in ways a quiet horse never does. Close off access to any adjoining field with weaker fencing, even if that shrinks the space for one night; a smaller, sound pen protects better than a large area with one doubtful stretch.
Using the Herd to Do the Settling
Never leave a Mustang to face fireworks alone if he normally lives with others. Horses read each other's bodies constantly, and one genuinely steady companion — an older gelding who has heard fireworks before and shrugged — can hold a whole small group's nerve. If your Mustang has a particular bonded partner, make sure that pairing is intact for the night rather than separated by your usual management routine.
Spread hay in several piles well apart so the horses can drift between them, heads down, rather than bunching at one feeder where a single big bang can send a tight knot of animals exploding in different directions. Fresh water should be somewhere the horse does not have to cross the most exposed part of the pen to reach, and a familiar radio voice from the yard adds ordinary sound between the bangs.
During the Night and the Morning After
Watch from a distance with a torch you keep pointed down, and stay out of the pen while the horse is running circuits — a Mustang in flight mode does not track people reliably, and your safety depends on the fence, not on being seen.
In the morning, check the fence again before assuming it held everywhere, and check the horse thoroughly: cuts along the chest and legs from wire, a shoe or hoof damaged on hard ground, heat or filling in the legs, and stiffness from sustained galloping. A horse who is lame, has a wound you cannot clean confidently, or is still not eating by midday needs your veterinarian.
If the Fence Fails and He Runs
Do not pursue a running Mustang directly; pressure from behind keeps him travelling and can drive him onto roads or into worse fencing. Alert neighbours and road users at once, share a clear description, and place quiet helpers at gateways and junctions while one familiar person works to get ahead and let the horse come to a bucket and a known voice. KinsLe's Lost Pet Alert System sends a free alert to nearby members as soon as you raise it, putting local eyes on lanes and fields while you coordinate the recovery.