Boundaries before everything else
Do the fencing first, because every other improvement is wasted on a tortoise who has left. Walk the perimeter at tortoise height looking for what he will find: gaps under gates, loose gravel boards, fence lines he can undermine. Tortoises dig with real determination and, given a corner where two barriers meet, can climb far better than their shape suggests. Bury a strip of mesh or edging a spade's depth along fence lines so digging meets resistance, block corner climbs with an overhang or a capped angle, and make sure the boundary is solid to the ground all the way round — a gap you would step over without noticing is a door to a tortoise.
The plant and poison audit
Before the first graze, walk the planting with fresh eyes. Common garden plants including foxglove, buttercups, yew and daffodil and other bulbs are poisonous to tortoises, and a hungry animal sampling new ground will taste things it would ignore in a familiar run. Remove or fence off what is toxic, and stop the chemical shortcuts entirely on any ground he will graze: no slug pellets, no weedkiller, no lawn feed-and-weed treatments, since residues sit on exactly the leaves he eats. If the lawn has been treated recently, keep him off it and let rain and time clear it before his first outing rather than trusting a guess.
Shelter, shade and water he can reach
Outdoor days fail on weather, not fencing. Give him a solid shelter — a small wooden house or cold-frame-style refuge — bedded with hay or soil, positioned where it stays dry, and make sure deep shade exists at every hour, because a garden that is shady at ten can be a suntrap at two and a tortoise caught in full heat with no retreat is in genuine danger. Sink a shallow water dish to its rim so he can climb in and out without tipping it, and place it in shade so the water stays drinkable. On stormy days and cold nights he comes back indoors; a first summer outside is a series of good-weather days, not a relocation.
Dogs, birds and other garden residents
Supervise around dogs regardless of temperament: even a playful dog can pick up or mouth a tortoise, and shell injuries from dogs are among the commonest reasons outdoor tortoises see a vet. Small tortoises also need a mesh cover over at least part of the run where crows, magpies or gulls are bold, since a light youngster can simply be carried off. Finally, think about what visits at night — foxes and rats both investigate an outdoor shelter — and bring him in at dusk rather than leaving the question open.
First outings are reconnaissance
Treat the first sessions as supervised tests, an hour or two in mild weather, and watch like a fencer rather than a sunbather. Note where he paces, where he digs hopefully, which corner he tries to climb, and fix those exact spots before the next outing — the garden is only as safe as the weakest point he has already found. Gradually lengthen the days as the fencing proves itself. If the fencing ever fails despite all of this, the map displays his alert from his KinsLe profile, with Lost Pet Alert System costing nothing in that profile, and a person who finds him can send you a direct message through the alert.