Here's a few ideas and points for you guys...
As far as where I like to sink structure goes, I try to sink some in very shallow water (2 to 3 feet) for the minnows and smaller fish to hide in, as well as for summer bass fishing. I also sank some evergreen trees and limbs tied together in deeper water (7 to 9 feet). Some of this is within casting distance, but others are not. The ones that are outside of casting distance from the shore are in areas that I prefer to ice fish around in the winter.
I'm not allowed to mark off brush piles with markers above water thanks to the real boss of the pond...the owner's wife. :') So, the best method I've found is to visually mark it off via FOUR different visual objects around the pond (IE: For finding one I line up a church steeple and the aeration stone, then two trees on opposite banks). I keep a map of the lake with these information written on it, along with dates when certain brush piles were sank so I can replace them in the future as they decompose.
Concerning PVC trees. I had an idea that should work well when you don't want to wait for the ice cover to melt, or when you have to sneak them in nice and quick to avoid friend's wifes finding out. :') You could cut a hole in the ice using a standard ice fishing auger and fold a flexible PVC tree to slip threw the hole. The tree could be built using a small enough diameter PVC for the limbs on it to allow them to flex up and against the trunk of it while you slide it in, then they'll flex back when they are threw the hole. You could ancor the tree by placing a brick at the bottom, hooked length wise so it too will fit through the hole. To make the tree stand upright you could either cap the top of the trunk to trap air, or tie a 2 liter bottle to the top.
