[NAGDU] Relief Area Odor

[David]

I made a river pebblestone area for Claire Rose to relieve herself.  It 
works fine for solid waste which I put into a Doggie Doolie (small 
septic tank).  I have tried using Simple Green outdoor odor eliminator 
on the pebble area, but it does not kill the odor in this Florida heat.  
The area is too big to use enzyme odor liquid on, because of the 
expense.  Does anyone have a solution that they have found effective?  
I've thought about hosing in some Borax.  Ideas?

David and Claire Rose in Clearwater, FL