I empathize, Scott, as I run into the same problem regularly. I think you've already taken the most important step, which is to go after only the most promising signals. It takes too much time and energy to dig them all. If you wear a loop belt or apron which allows you to carry an assortment of tools, you can try something that works for me on small to medium sized roots. I carry two long 1/4 inch square shaft screwdrivers which normally function as probes. But when I run into a tangle of roots, I insert them into the ground at opposite angles and test pull on them to see if the roots will separate. Most times they will give enough to allow a knife or small digging tool to get in there and loosen up some soil between and under the roots. When this is scooped out, the target is almost always in the removed soil. As a plus, this doesn't leave a large digging scar, just the narrow slit used to gain access.