I tried Clark's after Orkin didn't work out for me, and we ended up having rats in our attic again. This time the company doesn't do any changes to your house (Orkin had closed up a hole between the garage and the attic), and couldn't even refer us to someone who did do that. This service was just for setting up rat traps. We paid for the service man to come in 2 x in one week, then once a week for the rest of the month, to check and set up traps. It did work, but that was all we got out of it. We could have signed up for some extended service thing but we didn't and I got the feeling my serviceman didn't like that much. Now here we are about 6-9 mos later and we have the same problem. It is really frustrating to have tried two different companies and the problem keeps coming back.
Clark was helpful if you just want rats removed, but they may come back.