New Trap Idea: Oil Barrel/Slick for Slow

Watching valks destroy my base at warp speed made me think of this.

We have traps that eject troops and traps that damage them, but none that slow them down (well, not ground troops anyway - the air sweeper is not really what I'm talking about).

I was thinking of a trap that's a barrel of oil, knocked over when troops walk over it, and have their movement speed reduced by 50% (or 25%, would need testing). Hell, why not make it flaming oil when upgraded so it does some damage as well!

Just a thought, would be an interesting new game mechanic. It seems an obvious progression.