Write the sign for the driver you actually get
The driver at your gate is not careless out of malice; they are on a route with dozens of stops, following spoken directions, parcel in one hand, already thinking about the next address. Any strategy that depends on that person reading carefully and remembering an unlatched gate three minutes later is designed to fail. So the sign's job is narrow: one instruction, understood in a glance, at the exact moment and place of decision. Large lettering, high contrast, no more than a short line of text — and crucially the reason included in the same breath, because 'CLOSE THE GATE' is an order a busy person may shrug at, while 'CLOSE THE GATE — HORSES GET OUT' tells them what their small action is preventing, and people protect animals far more reliably than they obey rules.
Placement: both faces, at eye height, at the latch
A single sign on the outside does half the job, because gates are left open far more often on the way out — parcel delivered, mind gone — than on the way in. Put a matching sign on the yard side too, facing the departing driver at the moment they pull the gate toward themselves. Height matters: signs belong at eye height of someone standing at the gate or sitting in a van cab, not down at boot level where a parcel hides them and not above the gate where nobody looks. And place the main sign at the latch side, where the driver's hand and eyes already are, rather than centred on the gate where it reads as decoration. Weatherproofing is not a detail: a faded, peeling sign announces that nobody here maintains things, and drivers take their cue from that too.
Make the gate close itself
The strongest part of the system is the part that does not involve the driver at all. A gate with a spring or self-closing hinge swings shut behind anyone passing through, and a latch that engages on its own with an audible click turns 'remember to close it' into 'it closed'. Walk your gates as a stranger would: if any of them needs lifting, jiggling or knowledge to latch, it will be left ajar one day no matter what the sign says, and that is a hardware problem, not a signage problem. A chain and snap hook as a secondary fastening gives a visible, satisfying action for the conscientious driver and a second barrier for the horse that leans. Check springs and latches with your other fence checks, because a self-closer that failed in spring is just a heavy gate by summer.
Take the delivery out of the gateway altogether
Every delivery that can be completed without opening the gate removes one roll of the dice. A weatherproof parcel box or a designated drop point just outside the gate, signed clearly as the delivery spot, means the majority of drivers never touch the latch at all. Support it from your side: put 'leave parcels in the box by the gate — please do not open the gate, horses loose' into the delivery instructions on every order you place, so the note reaches the driver's handset before they reach your lane. Regular callers — feed merchants, the farrier, the vet — can be told once, in person; it is the rotating cast of one-off couriers the whole system exists to protect you from.
The human check that catches the rest
Even with all of it working, assume a gate will sometimes be left open and build the catch into the routine, not into luck. A latch check folded into the yard's existing rounds — morning feeds, evening lock-up — means an open gate is found by your people instead of by a horse at midnight. KinsLe's Care Teams makes that check accountable: set the delivery-day and evening gate rounds as assigned duties, and each completed round is marked with a timestamp, so on the day a courier has been and the gate check was somehow skipped, the gap is visible in the routine rather than discovered by the sound of hooves on the lane.