Peppermint oil sprayed like a flame thrower. Done. I am still waiting for my ultra sonic rat blaster. Scotty Kilmer recommends such. Those buggers just eat my plaster of paris mix like candy. Never a one has been caught in a Victor trap.
Rats are diabolically more intelligent than mice which is why your Victor trap did not work. They are excellent at managing to steal the bait from traps without setting them off. My exterminator brother recommends that you "think like a rat" when setting these things up, essentially you are trying to force the rat to touch the trigger mechanism either by strategic placement of the trap OR by placing objects around the trap that will force the rat to do so. Still they are notoriously intelligent and are very wary about "new" situations, especially if you are hunting a particular one that has narrowly escaped previous efforts.
I do not know that Peppermint Oil is effective as a deterrent with rats, it certainly cannot hurt as it is non-toxic etc. Rats are similar humans in dietary tastes: FATS, PROTEINS and SUGARS rule their world, also they need SALT. A good maple-smoked bacon will hit all four targets for the average rat. They also have a fondness for starches which are merely complex SUGARS anyway, slightly fried potatoes might seem like a nice treat...
Yours are outdoor, I assume? Do be careful with the use of poison in that situation: you may miss the mark and kill the neighbor's dog/cat instead. In this case you need to figure out what the immediate food source is (I promise it is not your Impala, that is just a tasty extra treat for tooth-sharpening: Rodentia teeth keep growing if they don't regularly chew something to wear them down).
Also, are you absolutely CERTAIN it is rats? Squirrels and mice are also known culprits for chewing on wires and such inside vehicles. If there is a cache of acorns somewhere in there it is more likely a Tree-Rat than the nasty Ground-Rat. Check droppings; mice vs rat are easy to identify:
If you are in a non-urban environment, have a spotlight and .22 scoped rifle: a night-time Rat Hunt can be tolerable provided you have a porch or something nearby and ready supply of beverages. You will want to bait the killing field, and likely your first hunt will be quite productive given that you are a good shot.
Don't flip the spotlight on and off, just leave it on and wait... your rats will magically appear eventually to feast on your very expensive bacon bait stations.
You might start preparing your victims for slaughter a few days in advance: set up feeding stations in spots conspicuous from your front/back-porch "blind."
A highly accurate scoped .22 caliber air rifle is better than gun-powder as it less likely to spook the rats.
If you are lucky you will get to see rat cannibalization, which is common! ~HAH!
Your other option is to discover where they are nesting and eliminate them there. I believe rat urine fluoresces under UV light (you might have to buy a chemical spray) and they sort of dribble urine constantly so the trail is easy to follow, and may also yield insight as to what they are eating besides your Impala.
That is your ultimate goal: discover what the FOOD SOURCE is that attracted them in the first place and eliminate that. Once that is done the rats will go elsewhere for their food, which is hopefully not a nearby neighbor's house or worse your house...
