I did see a show recently about a husband and wife team down in georgia who do nothing but help people get rid of dangerous snakes in their back yard. Ultimately it boiled down to that you need to get rid of their habitat. So they were having people keep their backyards well maintained - not allowing them to overgrow. Snakes need cover, so they are not going to live in the middle of a manicured lawn. Not sure the layout of your friends property. but it should be such that there won't be a lot of places for them to hide. In terms of the garden, they may want to space the rows of whatever they are growing much further apart then they have them now and keep the spaces in between mowed down.