Work out what is on the other side of the hole
Digging under a fence is purposeful, and the purpose tells you the fix. A dog tunnelling toward a neighbour's dog, passing walkers or the street is trying to get to something, and his holes cluster at gates and at the stretch of fence with the best view. A dog digging a shallow pit mid-garden and lying in it wants cool earth on a warm day, which is a comfort project rather than an escape plan. Young, under-exercised dogs dig because digging is deeply satisfying work for their paws and nose. Watch where the holes appear and what is happening beyond the fence at that moment before you buy anything, because blocking an escape artist and entertaining a bored digger are different jobs.
Secure the fence line so digging stops paying
For a genuine escape route, take the reward away. Dig a shallow trench along the base of the fence and bury welded mesh or paving slabs on edge in it, angled slightly toward your garden, then backfill firmly so paws meet resistance straight away. Large rocks along the base work where the soil is too hard to trench, and the gate gap, the most common weak point, can be closed with a threshold slab. Walk the line after heavy rain, because softened soil reopens old exit spots overnight. This is not about making the garden a fortress; it is about making the first few scrapes unproductive, so your dog stops investing in that spot.
Give him a digging patch he is allowed to love
Blocking alone leaves the urge with nowhere to go, so build the legal version: a sandpit, a spare border or a large low planter filled with loose soil or sand, placed in shade. Bury a few treats and a favourite toy just under the surface while he watches, praise him richly when he digs them out, and refresh the buried treasure regularly so the patch stays more rewarding than the fence line. When you catch him starting at the fence, redirect without drama: call him to the patch, bury something quickly and celebrate the right choice of venue. Most dogs move their digging within a couple of weeks once one spot reliably pays.
Keep the garden from becoming his only occupation
A dog left alone in a garden for long stretches will invent work, and excavation is a favourite invention. Bring him in for company, scatter part of his meal in the grass for a sniffing session, and make sure the walk and play happen before long garden time rather than as an apology after it. Check his paws after a digging spell for cracked nails or packed soil between the toes, and see your vet if he limps, licks a paw persistently or has broken a nail down to the quick. Neighbours and passers-by on the other side are worth a friendly word too, since their dogs may be half the attraction. To make sure the fence line actually gets walked every day, KinsLe lets you assign that check in Care Teams, where the person who inspects it records the round as complete with a timestamp for everyone else to see.