Know every identifier your horse actually carries
A stray horse is matched home through a chain of small details, and the chain is only as strong as its stalest link. The microchip carries a number a vet or warden can scan, but the number only leads to the registration database, and the database only leads to whatever phone number and address were last typed into it. The passport is his legal identity document, describing his markings and recording his keeper. A freezemark, if he has one, can be read at a distance by anyone who finds him in a field. List all of yours honestly: which database holds the chip, whether the passport details match the horse standing in front of you, and whether the freezemark registry still has you as his contact.
Audit each record as a stranger would read it
Once a year, and without fail after any change, read your own records like the finder who will one day rely on them. Dial the phone number on the chip registration — is it the phone in your pocket now, or a number from two yards and one house move ago? Is there a second contact, a partner or yard manager, who would actually answer if you were on holiday when he strayed? Does the address reflect where the horse lives, so a local finder is not directed to a county you left years ago? Most "unidentifiable" stray horses are perfectly identifiable; it is the humans' details that expired quietly underneath them.
Treat photographs as identification, not souvenirs
Markings are a horse's fingerprint, and photographs are how a finder compares them. Keep a current set: full body from both sides, face-on for the star, snip or blaze, each leg's socks and stockings, and close shots of whorls, scars, splashes of colour and chestnuts. Retake them more often than feels necessary, because horses change their paperwork constantly — a winter coat hides what a summer coat shows, a clipped horse looks like a different animal, and this spring's scar was not there for last year's pictures. Store the set with his records, not buried in a camera roll, so it can be sent to a vet, warden or finder within a minute of the phone call.
Make sure the yard holds the same story
Copies of the passport details and the microchip number should live where the horse lives: the yard office, the sharer's phone, your own records at home. Anyone who covers your horse — a sharer, a holiday helper, the friend who feeds when you travel — should know where his identification records are kept and what to quote if they get the call. If the horse is out on loan, both households should hold the full set, because strays do not schedule themselves around who has the paperwork. When the horse is sold, complete the transfers promptly and properly; the gap between owners is precisely when a stray falls through every database at once.
When details change, update them in a set order
Move house, move yards, change phones — and work the list in order: chip database first, since that is the record a scanner reaches; then the passport issuing organisation's details, updated as their rules require; then your own files and the yard's copies. If he ever does stray, report him missing to the chip database immediately so his record is flagged before someone scans him, rather than after. The finishing touch is his KinsLe Pet Pass, kept current beside the official documents: his identity, markings and your live contact details in one verified card you can show to anyone who has found him, anywhere, without waiting for office hours or database logins.