Dig routes:

The dig route is usually some form of a crossing route. I have coached on two staffs who ran them differently. The first staff ran a 10 yard vertical stem, followed by a post route for 2 yds, and then come straight across the middle just behind the dropping LBs. The other staff ran it with a 12-15 yard vertical stem and then come straight across the middle just behind the dropping LBs. It can be a very productive route if used correctly. You need to take care of two things for the dig route to be open. THe first is you need to somehow occupy the FS with some osrt of deep threat towards the deep middle third (i.e. post). You also need to somehow either suck the LBs up (i.e. with playaction) or keep them from dropping (i.e. some osrt of short drag crossing in front of the LBs). As a defensive coordinator, this route is hard to stop if you have a QB who can be protected and is patient enough to through through the window when his receiver is coming across.

Every dig I've ever seen involves running 5-7 steps upfield angling in at the deep safety as if running a deep post for 4 steps and then flattening out @ around 12y and dragging across to attack the deep holes in zone coverage. It's becoming a more common route in the shotgun-based offenses that are popular now. It takes a while to develop, but it's a pretty effective route.