Have a client who owns a fenced in 2 acre commercial storage area with the buildings and various vehicles on it. No trees or shrubs. She wants me to attempt to kill all the vegetation growing. This is all rock. Needless to say its difficult to mow and would look better to see just the rock. Would like to use something other than Round Up so I wouldnt it have to apply it 3, 4 or 5 times a year. I have a back pack applicator and a 20 gallon sprayer which i can put on a 4 wheeler. What can I apply? Can it be used directly on the existing growth. Need something that I dont have to water in.