It's not as bad as it sound really.

My Floating Castle Mod (Aezeal's Castle) has a problem. I've placed some architecture up in the sky, that stays there as intended (with no Havok box ticked). If I play I can walk around up there without problems.
HOWEVER it I put my 4 Dwemer Guardian Spheres up there to patrol a bit I ALWAYS find them beneath the castle on the ground (fighting mamoths). I've ticked their no havoc boxes too but it didn't help.

How to fix this?

Did you put navmeshes on your castle? Did you create a patrol path for your spheres?

Also, when you placed them, did you by any chance place their feet/bottom piece slightly inside the floor? This can cause problems as well.

I did not do navmeshes I'll have to admit. I did place them on the ground and not inside the floor and I did set a patrol path.

I'll look into the navmesh, but shouldn't they atleast appear on the castle proper and not below even without the navmesh?

The actors can only follow the Navmeshes that are available. I would assume it's either a mesh going into the ground, causing the actor to fall, or there is no mesh and the actor falls to the only one it sees at its position.

Well that could explain it, my dragon pet's didn't suffer from it but they are flying of course. Later when I can start up the kit I'll fix it (navmeshes I think I can do that from the tutorial) and let you know about the result.

Navmesh helpt thx (though getting them w/o errors is.. hard

It took me a while to get the hang of Navmesh.

Here is a http://geck.gamesas.com/index.php/gamesas_Tutorial_Navmesh that is just good reading. I don't suppose it's much different in Skyrim...I could be wrong they may have included some changes/improvements.

I've read the creation kit navmesh tutorial. I first let it do it automatic but there where HUGE gaps en loads of islands. So I've done some by hand. I still get about 50 error when saving though. Might be due to the fact my castle if floating over another navmesh.
My guards stay on my castle though and they find eachother (actually they have been killing eachother, I had hoped putting them all in the player housecarl faction would make them friends.. but that didn't work, so I've added the player faction too.. hope that will work, guards killing eachother doesn't make a good castle defense.

Grrr now I wanna make a castle... Thanks now I have to stop my temple project to make a castle . Also Navmesh is very important, make sure it's everywhere you want your gaurds to go.

Hmm that was to optimistic it seems, While I found all 4 of them fighting on my castle before I changed the faction I now find 3 of them on the ground beneath it again (not attacking eachother though)