i remember something like this is that Splash-Damage-Bound or something it had tanks on the side and a bunch of dark templars Set to AI status junkyard dog walking around doing splash damage and trying to get through it.the only problem is that those block you when passing them while you could have Lurkers rapidly change From ally to enemy slow enough for a couple tanks to shoot them so it would look like this
Z=lurkers burrowed switching ally to enemy status X=any terrain

Z X Z X Z |
X Z X Z X |
Z X Z X Z |
X Z X Z X |
Z X Z X Z |
X Z X Z X |

sorta like that or something with tanks on floating terrain on the side/with the |=tanks randomly shooting alover

NOTE: i dunno if somebody allready said this i just felt lazy ;p

But then whats the point of the lurkers/non-targetable zerglings?

I skimmed through the posts, sorry if this idea has been posted....

So, why not just have a burried unit, a junkyard dog observer, a location constantly following the observer, and the unit burried constantly following the location?

Because then the tanks simply attack that single spot, and with units that can pass over eachother, you can't have a location follow each one individually.