It's pretty important to state where you live and what ants you're dealing with, lol. You can give a brief description to help ID the species. Digging for queens is a very tiresome and poor way of finding queens, it's only best to do so when you've found the evidence of a queen having dug her first claustral cell, which takes a bit of experince to differentiate between nest entrences of small or established colonies depending on species. I can't help much without more info about your area, but keep an eye out on warm and humid days for you area. Different species fly at different times of the day, and here in Florida, many tend to fly at night, but taking lots of walks around areas with less human activities is a good idea. Especially in areas where freshly mated queens are easily spotted, like on bare ground, pavement, and such.