Originally Posted by Grandy
Yes it is, but that is only after they stumble upon it. After everything is set up and upgraded, tele and dispenser included, the fact the can see you is second to the fact they have to destroy your base and stop your team from completing the objective at the same time. In other words they have to split their forces. And taking down a well-positioned lvl 3 base is thougher than taking down a mini-sentry base.
I suppose your method of ninjaneering is good as well, though if I ever saw a lonely minisentry, I'd stick around until I can see the corpse of whoever built it.
actually, this is something i do quite often. there's my teleporter-dispenser-"base" hidden behind one corner (if i really want to be safe, i place the teleporter a little further away, so that when my freshly teleported teammates reach enemy sight, they're not glowing anymore, giving away the fact there's a teleporter), and my minisentry and i obvious in the other corner. then they shoot my minisentry and get a couple of my shotty-rounds in their stomachs, after that they pursue me (plonking down more minisentries on the run while continuing to fill their bodies with lead). after that, they're either dead with no idea where my important stuff is, or i'm dead and they still have no clue where my buildings are (actually, they tend think they got me before getting my base up). all i need to do after that is teleport back to my location and repeat. i can manage to keep my base alive for pretty much as long as i want like that. my strategies tend to involve more psychology than brute force.