That last post reminded me of something I have been meaning to post for a while. We have, in the higher levels of wspace, an invaluable capacity for safe PVE. That is to close off a system to almost all outside influence. You do this by popping all wormholes entering or leaving that system. I refer to doing this as "zipping up" the system. Note that all wspace system will naturally zip themselves up, because their static (and any other incident wormholes) are always going poof via timing out.
It is certainly possible that there is someone already lurking in your zipped-up system, cloaked and waiting. I have heard of hunters who do this. However, in all my days of doing stuff in zipped up wspace, I have never had it happen to me. I think that restricting one's hunting to a single system is just too boring for most pilots.
A zipped up system is not absolutely cut off from the rest of EVE. Wormholes are dying and being regenerated elsewhere all the time. But the rate of this happening is not very high; days can pass without a new wormhole showing up in my C4 system. (My impression of rates is that C1s don't get that many incoming wormholes; C2 and C3 get more than C4; C5 and C6 get fewer but when they do get them, they are very likely to be happening as an intentional wormhole reroll from a group of pilots who know what they are doing and are very likely to want PVP.)
To be assured that you're not being sneaked up on, you should always keep the discovery scanner where you can see it. You'll see a new signature almost as soon as it happen. (This is a bad game mechanic. Boo, CCP!) If you ever see a new sig, and you are out and about doing stuff, that's your cue to hotfoot back to safety. Get a scanner ship out and see what the new signature is. If it is a wormhole, it is very likely that someone will come through. Prepare yourself. If it is not a wormhole (which is unlikely, but it does happen), no problem. Get back out there and continue doing your thing.
The concept generalizes to sets of systems, although usually this means having to put a cloaked scout to watch an alien tower.
Want to mine in wspace? Zip up your system.
Want to run sleeper sites? Zip it up.
Want to do PI without having wandering monsters pounce? Zip it up.