Hey buddy I owned you omni previously,and i had same rat issue,for months,i lost some 8k for my omni.That was very high for it.so next time i got it service,got some advise from regular mechanic that spraying some oil on engine bay help to keep engine compartment clean.So i done it,there after i did not notice any rat problem in my car,infact,there after they never gave me any problem,even though they roamed near my car.
Another case was my uncle who owns Maruti WagonR,he need to park his car which is exactly beside the restaurant,i bet his engine compartment looked the worst even it was 2 year old car.He had done almost all the methods,tabaco,jelly trap,mouse poison cake ,nothing came to rescue. those mouse did not gave up,i just hated to look his engine,pathetic. my dad advised him so,to spray some oil,he had done it in his service and results were positive.He was so happy he drove down to our home to show us. hahahha.
Still story continues with my ertiga
,now it is also infested,got rid of them,but not with oil.