Over the counter rat poison , which ?

I've spotted a couple of rats and laid about 4-5 traps in the back garden and also an enclosed bait tray station. The bait tray station came with 4 blocks that sit on the spikes and I put some more bait inside , leftover loose stuff and it's all been eaten.

I'm going to have to get some more so which would you say is the most effective over the counter rat poison ?.

an air rifle be ok on the long tails as some of the poisen now the rats are immuned to it
I had a couple of rats at weekend so I got deckchair out some cans of beers and air rifle took both of them out

Sent from 2 tin cans and some string