If you buy a house in the country there's going to be some form of critters, Snakes can go through over or under a fence. They can even climb trees.
Rattle snakes do not dig holes to live in so unless they went in there to catch and eat whatever made the hole, or moved in when something else moved out.
If you have that bad a fear of snakes then you may be better off living in the city because from time to time you most likly will see one.
There really is nothing that's going to keep them away. Moth Balls works for some breeds of snakes but not rattle snakes.
Just make sure there's no loose siding or holes in the foundation to let them in and you will be fine.
I had one customer who recycled, or repurposed everthing, bought rain barrels to collect water, bought CFC light buld to conserve energy. She also was a big time gardener and had at least 50 flower beds. But refused to have a compost pile because she thought there might be a snake in it. So instead at the end of the year she had a pile at least 12' X 12' by 12' high of old vegitation that she would burn and waist all that free compost then go out every year and buy a truck load of bagged compost.
She had an old building that she used as a green house and potting shed that she had me burn down because she saw one black harmless snake in it.
She saw one racoon in the yard one night and wanted to sell the house because of that one critter.
The critters were there first.