There are supposedly safe products on the market for this, but I never quite trust them. Some of the traditional methods, Like beer traps and sharp sand, do help control slugs. So does picking them opff by hand. Go out on moist evenings, pick them up, put then in a binbag and post them to your mother in law. One safe method of control is nematodes. You can buy these biological contol agents, and they can be very effective, and are animal and child friendly.
Copper. Slugs and snails hate copper according to the perpetually grinning A.Titchmarsh. It is rather expensive but you can encircle precious plants with ground-level "collars" made of copper- available from some garden centres. The slugs hate touching it for bio-chemical reasons. Perhaps regular copper piping is worth a try? Would be much cheaper.
going on from mez's reply copper wire - house wiring cable, if wound either round the top of a pot or encircling the plant, the ends twisted over & buried in the soil will give the slug/snail a mild electric tingle and make it go & eat something else - never bl**dy weeds though is it!