How to keep Copperheads away from my home

Question
We have killed 3 copperheads in the last 5 weeks.  I live in Dallas County in Texas and two have been on my back patio and one was on my front porch.  We have a greenbelt behind our home, and keep our grass trimmed at all times.  We do not have a bunch of places to hide either.  Our neighbor (2 houses down)lets their grass grow very high and their yard is cluttered.  It seems like the last two times they were working in their yard, these snakes showed up at our house.  My husband put down sulpfur but it has not worked so far.  Also, do you think there are a bunch more?

Answer
OK, please don't take this the wrong way, but are you 100% sure they were all copperheads?  I ask because I can't tell you how many times I've been called to remove a "coral-backed-rattle-moccasin" around here only to arrive to find a harmless corn snake. I suppose it doesn't matter to many people what kind of snake it is period, but positive ID might make you feel better.  So let's assume you're positive and go from there.

Copper Heads are venomous, but it is a very mild venom and they are not super aggresive.  That's the good news.  But, if you have kids or small pets they could definately cause a need for medical attention.  That's the bad.  

There is no product you can put in your yard to keep the snakes out.  However, guinea fowl are know to kill snakes, especially small ones.  They are also good at cleaning up insects and weeds in your yard.  So, perhaps a few birds are in your future!  That would be the best advice I could give you.