httpv://www.youtube.com/watch?v=l8UlP_V_6O4 No chemmies needed! Add sawdust instead. I'm not sure it needs to be underground, but WOW that's a big hole! Having another compost bin specifically for the pet waste like the one you have for your food would also do the trick.
I was walking around the other day and found these massive 5' x 5' x 5' compost bins. I hope they don't always look this inactive! There's a lot of potential here. The "death" of a compost bin is when branches are tossed in... while they are organic and will break down, they will take forever to do so in that form and just take up space. To the left of these bins is a nice pile of wood chips, and it was good to see that the wood chips were not present in the bins... sawdust yes, wood shavings not really, wood chips no way. If the nature area wanted to (and maybe they do on a scheduled basis), there was plenty of material in the immediate vicinity of…
Just the other week, I had filled the bin up to the edge with new material...and I look out there today after forgetting about it and it's dropped nearly a foot! This is what I love about compost piles- I've been adding material to this thing on a weekly basis and it's just a bottomless pit of degradation. With the summertime coming on, I can only imagine this process will kick up a few more notches still.