No Rats in Alberta.
But this place has a problem with Pocket Gophers :
http://talkaboutwildlife.ca/profile/index.php?s=553I've tried many ways to kill them off, and the best one so far is to dig the opening(s) up (with care) and put the end of a hose down hole, for a 20lb propane tank. I then place dirt over the hose at surface level and turn the propane on. Let run for about 3-4 minutes.
Repeat at other mounds/holes.
So far, it has worked every time.
Propane, being heavier than air, will settle to the bottom of their tunnels.
When the rodent passes through this gas cloud, there is no air to breath, so it kills it.
Should work well on Rats as well.
Beware of any open flame or other ignition source. Propane as a gas will settle to the lowest point, even above ground.