Start with scent, texture, and safe planting
A sniffing garden works because a dog experiences the world nose first, so design the corner as a sequence of smells and surfaces rather than a display bed. Cluster sturdy pots at dog height with robust, dog-safe herbs he can push his face into, and intersperse them with patches of longer grass left unmown, a section of bark mulch, smooth stones, and a patch of bare earth, since each surface holds scent differently and slows him into investigative mode. Check every plant against a reliable dog-safety list before buying it, keep anything doubtful out entirely, and never apply weedkillers, slug pellets, or fertiliser in or near the corner.
Lay it out as a slow circuit, not an open patch
Arrange the pots, textures, and a low log or two as a winding route along a fence or around a tree, because a path with turns and pauses holds a dog's attention far longer than a square of planting he can survey in one glance. Tuck a couple of features at different heights, such as a raised planter he can sniff up into and a sunken tray of sand at ground level, so the circuit asks his nose to work high and low. If your garden is small or you rent, the same circuit works on a balcony or patio using pots, a planted trough, and a washable snuffle mat at the end of the route.
Load it with small discoveries and rotate them
The corner becomes enrichment, rather than scenery, when it hides things: scatter part of your dog's normal food through the long grass, press treats into the bark, and wedge a favourite toy between pots for him to locate. Refresh the hiding places and swap one or two scent features every week or so, perhaps a pine cone collection after a woodland walk or a different herb in the spare pot, because novelty is what reawakens a thorough sniff. Let him explore off lead if the space is secure, and resist calling him away mid-investigation, since uninterrupted sniffing is the calming payoff.
Supervise the gardeners, canine and otherwise
Watch the first sessions to see which plants he merely sniffs and which he tries to eat, and move or remove anything he grazes on persistently. Check pots for standing water after rain, lift any mushrooms that appear overnight before he goes out, and fence the corner off temporarily if you must treat neighbouring beds. When a feature flops or growth changes with the season, put a follow-up question to KinsLe's Kimmy; she answers using the KinsLe Answers library, which can suggest the next rotation to trial.