Just adding my two cents, I'm a baby in the caching world (joined june 19th 2011) but I'm fully addicted and look for ways to get more involved in the hobby all the time, outside of looking or hiding. Unfortunately work has been getting in the way a lot.... Anywho...
I've seen many a cache that, while it wasn't buried, it was inserted into the ground. It has spawned many an idea in my head since 'it wasn't buried' nor did any of them require a pointed object to place it or retrieve it. Before moving forward with any of my ideas I directly called Groundspeak to inquire about the caches I have found just to be sure I was 100% clear on any gray areas of the rules. No I didn't give them names or cache IDs, I just described the things I've found.
I have found sprinkler head caches and see them for sale on websites. I asked about them specifically and they are illegal hides. They require a hole. You CAN make an impression in the ground and place a container in it, then camo it with natural camo but anything that needs to be pounded into the ground or a hole created in order to place it is an illegal cache.
Back to the drawing board for several of my ideas but I welcome the challenge. I love hides in plain view and it's actually just as much fun coming up with them as it is finding them.
I may or may not have helped but I just wanted to add my two cents since it's easier to make a spot to hide something rather than find a spot to hide something.
Good luck to you Furnache.