A mate of mine got into pest control a few years ago...He started using a system where you fill the runs with gas then once you have enough gas in the runs you press a button then BOOM vermin gone...Only thing was how do you know how much gas to put in the runs? Well the first job he did he pebble dashed a customers landrover and burnt his eyebrows off and all the hairs on his arm. He stopped using this as he could not calibrate it...Ha Ha
We have a variety of things my father inlaw uses in France. He has a 'mole man' but he failed to get rid of them in the main garden area. There is plenty of land for hem to go and dig but just one particular place that has a reasonable lawn.
We used to use the gas but that proved tricky, not sure if you can get it here though. You dig a small hole over the newest tunnel and set the gas so it goes down the hole. (Its a dense gas)
The newest one and the most expensive is the afore mentioned explosive and boy do they work! Its like a small fire work and you certainly know when they have gone off. Im sure you could probably import them? IF not i could bring you some back when i go next time?