Hi,
I had rats in my garden and my compost bin a few years ago which moved there from a neighbouring pig farm. The things that rat killer man from enviromental health told me were,
Rats are smart. They only eat a little of any new food and test the effects. If it dosent hurt them they tuck in. So a poison needs to be potent in order for a small amount to kill them.
Once they have a food supply that they trust, they wont eat anything else unless that supply runs out. So you need to prevent them getting hold of any other food in order to get them to eat the poison.
The rat poison that enviromental health officers in my area were using at the time could be neutralised through the digestion of foods containing vitamin K such as peanuts. The rats instincively knew this and would scale a wall and climb a tree to get to the nuts in the bird feeder. So bird feeders of any type had to be removed.
Although they are suspicious of some things they have an insatiable curiosity around others and cant resist anything in a bag. So placing poison in a tied up plastic bag inside a compost bin for instance would persuade them to eat it.
The colour of the poision is a result of the dyes used to prevent it being confused with animal foodstuffs.
The things that worked for me were,
snapper type rat traps with a lump of softened mars bar pressed firmly on the spike and then allowed to harden again. Rats are fast. Anything that can be easily pulled from the spike, springs the trap but spares the rat.
And...
Neosorexa Gold available from the feed merchants. place it in a piece of pipe against a wall or building and check it every day. Dont let it run out. While ever they are eating it , keep feeding it to them.
And...
A couple of cats who love to hunt
I did notice that Ascott supplies were selling battery powered, electric rat and mouse killers which seemed like they would be effective.
I hope that helps