Carbon Monoxide Injection For Killing Underground Rodents

I was recently asked about the new carbon monoxide smoke injection machines for killing rodents recently and I decided to try one out. Found this link from U.C. Davis. It didn't fair too well for these expensive ($2300 to $5000) exhaust smoke machines, but I wanted to give it a try myself. They do have a higher operating cost and they take about 15 -20 minutes per hole. They also _Require_ that the ground has to be moist ( which in the western states limits the use to maybe spring time ??? To me the rate of success was not high enough.
(efficiency = 66%)
The rodent control machine was ineffective against California ground
squirrels (efficiency = 15%). It was less effective in dry soil conditions
The smoke oil is about $1 dollar per hole. ( The oil makes smoke and is used so that you can see where the smoke / fumes are leaking out of the tunnel and you have to seal off any cracks or holes. This is apparently why you must not wait until the ground is dry or you will not have any success because the C/O will be leaking out of the grounds cracks. If the carbon monoxide doesn't stay at a high enough percentage in the tunnel for a while, the rodent doesn't die)

The thing that bothered me the most was that the rodent hole was still there even when the rodent dude was dead. The other rodents will run in from the neighborhood and take back over the tunnel leaving you to wonder if he was really dead or not. : (