Mouse Traps: Place mouse traps in the garden. And with the good bait you will catch them. Also if you know the entrance or the exit or the burrow of the rats then place the mouse trap there as well.
You can use cage based trap and spring based traps. Glue or baits will not work outside much.
How to know you have rats in the Garden…
Holes in the ground
The places to check for rats in the Garden:
Garbage bins: For foods the rats might be found in the garbage bins.
Sheds: Sheds are mostly made of woods and rats could be found there too.
Bird Feeder: For food the rats might be going in the bird feeder, so keep checking in there.
And here are the best rat killer powder in India that you should know of.