Yes, you can teach your rattie to walk on a leash. Make sure that the harness fits the rattie properly and use a short leash to start. Train the rattie inside just in case the rattie would "slip the harness". Never, I repeat, never use a collar on a rattie. For a collar to be tight enough for a rattie not to get out of... it would do serious harm to the rattie, if not kill it.
DELUXE VALENTINE'S DAY PIRATE COSTUME WITH MATCHING PIRATE HAT
In the high plains of South Dakota, USA