Which makes it so, my unit randomly attacks 10 random regions. He randomly chooses a region from 10 (Random). Do you understand my basic english?
Place your 10 regions in a region array size 10, starting with index 0 and running up to index 9. You can then get a random region by using the variable with a random inclusive integer between 0 and 9 as the array index. This solution is extremely efficient and if you define a constant for the array size it can be very easy to add or remove regions as required.