I read this in New Scientist, I believe.
Take a battery that's apparently drained (doesn't work in your walkman anymore, for instance). It will most likely have some sort of voltage left in it, though.
Put the battery on the ground near your precious strawberries. Connect a loop of un-insulated wire to one end, and another to the other end. Place the loops so they are around the strawberries, one within the other, so the wires are within a few millimetres of each other.
Now, whenever a slug smells your yummy strawberries, it will get an electric shock if it tries to approach!
Haven't tried this, but I thought it was worth mentioning.
Kae