Ground Hornets

So I was removing Ivy from a 24'x8' bed and was suddenly swarmed by ground hornets. I called the pest control company I deal with and had them come out to check the area, and they couldn't find anything. I want to go out to continue working in the ivy bed, but don't really want to get swarmed again (It hurt just a little). Are there any tips to getting rid of ground hornets? These things were about 1.5-2" long, and I was stung several times through two layers of t-shirts. I did not see any holes in the ground, so I don't know if they were passing through, or they are located in close proximity to where I am working.