3-4 shell robber coverage vs 2 back slot

we do a couple different things. In general, I try to always hold the 2 shell regardless of the formation. We will sometimes use the corner on that side as the robber player and roll both safeties to a cover 3 look behind it. Your OLB can play the underneath route and redirect if needed. Its good because it confuses the hell out of the opposing QB who at first is expecting a 2 coverage because of our alignment, then is getting a wrinkled version of over 3 where the corner is playing the under routes of the #1. Lots of passes defenesed and a few pics just out of this coverage.

You are a little more susceptible to run game that side.