I would first find other ways to deter them from chewing. Offering blocks of wood, giving them hard things to gnaw on. Making sure the rack is built sturdy and flush with no gaps for the rats to get a hold of.
If you can narrow it down to one rat, you may have to think about keeping them in something else. Rats will learn to chew if one does it.
You can try the deterrant, you may find it breaks them of their habit. I personally never used it because I didn't want to waste money on it if it doesnt work LOL. But! Luckily none of my rats chewed their tubs.