btw: be sure to ask for the kind of repellent that's safe for garden plants.
I believe it is a combination of rotten egg, garlic and some other foul smelling stuff.
Red pepper also has worked well for me and on more than one level (two legged pests learn to stay out of an area that has been red peppered, they never know what got them ...just that it hurt and not to go back) but it does wash away with the rain or blow away in time with the wind.
edit to add: to keep the two legged pests away you pepper the obvious entrances to your patch area, if they find the plants red pepper won't stop them, but it will be a little payback.