Hi S.,
We had this problem in a house we lived in. We bought this stuff at Lowe's. They are pellets in a green bag that you sprinkle in the yard around the house. A few days after sprinkling the stuff, there was a significant difference. In another home, we had to do the same thing, but we had to spray as well. We had terminex come out. If you do that, just be careful. The chemicals are safe, but they require a contract and will come out when you aren't home (they did this to me, and were coming out and charging me after my contract was up). You can also get the same chemical by going to your local exterminator. They sell pretty strong stuff in gallon containers. The stuff is safe after it is sprayed, but to be on the safe side, make sure the kids are away and the pets are outside when ou spray. Spray the perimiter outside about every 3 months, and inside once or twice a year.