I find that at high level play, most of the victory comes in the planning. Reconnaisance (especially divinations) are the key to not being caught off-guard. In an environment where a single save or full attack is all that stands between a character and a dirtnap, knowing what you're walking into is absoutely key.
The painful part of DMing for this kind of campaign is that you need to spend a lot of time preparing a thorough defense against hostile forces. You need to flesh out hideouts, minions, magic items, tactics, contingency plans, etc... natural selection puts the NPCs who don't defend themselves properly out of their misery quickly. The most painful part is that as DM, you won't be able to anticipate the tactics the PCs will use to overcome your defenses, not the first few times anyways. Sure, the obvious ones can be foiled, like flying in through the window of the second floor, or sneaking in invisibly, or the old scry-teleport trick. Only after having all of your carefully placed traps and such thwarted by an ingeniously simple plan half a dozen times will you finally be able to truly pose a challenge to the PCs. And make sure to fight dirty. It's truly amazing what a PC of that level is capable of when put to the test. Remember, knowledge is power, and recon information should be more preciously guarded than the royal treasury.
-nameless
The painful part of DMing for this kind of campaign is that you need to spend a lot of time preparing a thorough defense against hostile forces. You need to flesh out hideouts, minions, magic items, tactics, contingency plans, etc... natural selection puts the NPCs who don't defend themselves properly out of their misery quickly. The most painful part is that as DM, you won't be able to anticipate the tactics the PCs will use to overcome your defenses, not the first few times anyways. Sure, the obvious ones can be foiled, like flying in through the window of the second floor, or sneaking in invisibly, or the old scry-teleport trick. Only after having all of your carefully placed traps and such thwarted by an ingeniously simple plan half a dozen times will you finally be able to truly pose a challenge to the PCs. And make sure to fight dirty. It's truly amazing what a PC of that level is capable of when put to the test. Remember, knowledge is power, and recon information should be more preciously guarded than the royal treasury.
-nameless