Okay I went and had a look at the Spotless book. If you are thinking about the snake poo option, apparently it is a small pellet that doesn't smell and it should last about 12 months. You scatter it under the house or in the ceiling, it says.

There is also a mention of naphthalene flakes used to deter a rat...I believe this is the same stuff mothballs are made out of... but to counteract the smell it says you can sprinkle some lemon thyme along with the naphthalene.