New dark spell - protection spell

Since dark spells lack any kind of hp related effects, I thought of a dark spell, called protection spell..yes it sounds a little odd but Supercell has the last say naming so let them sort that out. The way I think it could or should work is just an idea, so feel free to add to it. I think it should work similar to the Grand warden ability where troops in its aura will not take damage for 3 seconds on lvl 1 and 5 seconds max lvl. Actual times will need to be reviewed obviously or it will be over powered. I think it's a great idea for a spell. The obvious downside is if you just building those u could walk through a base easily so it will need to be tweaked and tested before. Maybe limiting the amount u could build, or make it so that the only way u could have one is via a donation from a clan mate.