New Item - Invulnerable Ward

This is a concept I've been thinking about for a few days.  I'm not sure of the exact costs, durations or limits of it yet but I thought it would be interesting to have a third kind of ward to make something like Rock - Paper - Scissors.  Essentially, an Invulnerable Ward would last it's full duration in the spot it's in no matter what.

The idea would be that Sight Wards counter Invulnerable Wards because they do the same job at a lower price.  Vision Wards counter Sight Wards because they can see them but the Sight Wards can't see the Vision Wards.  Invulnerable Wards would counter Vision Wards because Vision Wards wouldn't be able to kill them at all, making the Vision Ward a waste.

There are a few different ideas I had for Invulnerable wards to balance them.  They could either cost a lot of gold, have a lower duration and/or could have a team limit (meaning the team as a whole could only have a certain amount on the map at once, maybe even only one).

I really like the idea of a trinity of wards for a few reasons.  One, it would give more ward counter-play options.  Instead of having to fight fire with fire (magical sight vs magical sight) you could avoid the fire altogether.
Another reason is that it gives guaranteed vision.  While many might think this is a bad idea in itself, I think that guaranteed vision allows more options for teams to play well.  If one team is incredibly far ahead, can afford vision wards and oracles and consistently clears the other team's wards, the team that is behind is going to have an increasingly hard time turning the game around.  And while many might say this is fine, one of the reasons that I like LoL is that turn-arounds are so possible.
Just think about the mechanic of inhibitors.  Yes, they make your lanes push and help you to siege turrets, but they also force your own minions to get to the other team at the same time.  And if you aren't actively using them for siege purposes it actually helps the other team to get gold/exp without having to overextend into lanes.
Invulnerable wards would help in somewhat the same way.  They would give a team vision despite being outdone in terms of magical vision.  They would allow for a lot more playmaking when you're behind.

Obviously this idea would need a lot of tweaking and tuning but I believe it could be a very good addition to LoL.