My problem with Regulus mines happens to be twofold.
1) He can use them as grenades. Sometimes I can dodge this, but usually I wind up taking a fair amount of damage. Usually the amount of damage tends to leave me with enough hp for me to die via snipe.
If your talking about how he uses them as "grenades" then if you get hit its only your fault. As soon as you see him start the animation or throw the mines move out the way and it simply wont hit you. And bang, he has just wasted time chucking mines.
2) If I can see them I can't do anything about them. Oak flags and Regulus mines should be destructible by attacks... Unless I'm a general, but this means that Assassins are at a disadvantage versus a mine-based Regulus.
if you have one general on your team, get them to buy level I minataurs (for something like 350). Use them to scout/detonate mines. You make mines completely useless if you do this.
Not just that, Stardock/GPG have been kind enough to chuck in some 50g totems that allow you to see them. If you can see them, why dont you just go around them?