The rule itself: a door is open only while a hand is on it
State the rule to your sitter in exactly those terms. A vivarium door is never propped, rested, or left swinging while they turn to pick up a food tub or a water jug. It is either latched shut, or it is being physically held open while their eyes are on the animal inside. Reptiles do not announce an escape attempt. A gecko that looks asleep can be up a sliding door track in a second, and a snake investigating the gap its keeper just left will be through it before the food tub is open. The rule removes judgement from the moment: there is no such thing as "just for a second."
Why feeding rounds are the risky moment
Feeding rounds concentrate every escape risk into a few busy minutes. The sitter's hands are full, their attention is on measuring food and watching several enclosures, and the animals themselves are at their most active — feeding responses are aroused, snakes strike toward movement near the opening, and lizards come to the glass expecting food. A door left ajar during rounds is not facing a sleepy animal; it is facing a hungry one already moving toward the opening. That is why the rule has to be drilled specifically for rounds rather than mentioned as general good practice, and why one enclosure at a time, fully finished before the next is touched, is the working method.
Walk one full round with them before you leave
Do not just describe the round — do it together, with you watching. Have the sitter open the first door while you point out where the animal usually sits, how fast it moves when food appears, and which way the latch or lock seats so they can feel a proper close rather than a near close. Show them the pause that matters: after the food goes in, wait until the animal has turned away or settled on it before closing up, so nothing is trapped in the door track and nothing rides the door out. Then have them run the whole round back to you, start to finish, while you correct the small shortcuts — the door held with an elbow, the latch left for later — that appear when someone thinks the method is understood.
Set the round up so the rule is easy to keep
Most door lapses happen because the keeper needs a third hand. Remove that pressure before you go: portion each feed into labelled tubs in advance, put a water jug and a cloth within reach of the enclosures, and clear anything the sitter would otherwise set down mid-round by opening a door wider. Keep feeding tools for each enclosure beside that enclosure, so there is no carrying food across the room past open doors. If several animals are fed on the same round, write the order down — the most active feeder first while the sitter is freshest, or whatever sequence keeps doors opened fewest times — and make the latch check the last action of each enclosure: close, latch, gentle pull to confirm.
What to do if a door is found open
Rehearse this too, because a sitter who finds a door ajar and an animal missing needs a plan, not a panic. First, close every other enclosure and the room door. Then search warm, dark, low places close to the vivarium before widening the search, and put a shallow dish of water on the floor nearby. The sitter should call you straight away rather than spending hours searching quietly out of embarrassment — the first hour is when a lost reptile is usually still close by. Writing this sequence into KinsLe's Care Pass, alongside the door rule and the feeding order, means the sitter can follow the whole routine — and the emergency version of it — without relying on remembering a conversation.