I have a use for Slingers just now that was found by accident! I put them at a 30deg angle (ish) at the right side of my front line so they are facing out towards the enemy (so front line looks like _ _ _ _ _ / ). Behind them I have one infantry unit just hanging around (any infantry) and one or two cav near that but a little back (if no cav then more infantry).

If the enemy engage my front line my slingers can fire away happy and get free kills down the line and not hit my troops. More often though they become the taget of an approaching enemy unit. It doesnt matter what or where the enemy unit is, the intention is so obvious I have loads of time to start my infantry behind them charging forward to intercept and then run the slingers back a bit to safety (turning fire at will off!). Once they are tied up in melee the cav then manouvers for the flanks. It works great for disrupting an enemy formation since they seem to like taking the bait at any cost, usually with a cav unit but also with units from the middle of their formation. It creates opertunities which is great. Only tried it with a front line 5 or 6 units long so far.

Once the unit is minced I run the slingers out again to the same position to either re-run the trap or fire at will where they can reach right down my line.

The other units involved in the trap either go back again or if my front line is fully engaged they start with the hammer and anvil routine.

The infantry type behind doesnt matter so long as they can be relied on not to rout - they are there to tie up the enemy unit.

And (!) it works both for defensive and offensive action. So far. Hurrah!