I have a toilet trained Bengal. He uses the toilet whether the lid is up or down. :)

He also like to use anything that looks like a toilet like a bathtub or a shower. I put a cafeteria tray in the shower for his convenience, but want to keep him out of the tub.

I started with pepper sauce, but when that dried, it looked like there had been a murder with alot of blood stains...

Then I tried keeping a mixture of vinegar, lemon juice and black pepper in the tub. That worked, but I worried it might eat the bathtub glaze over time. Then I put aluminum trays and sheets of aluminum. That worked for two weeks. Now he no longer fears it. I sprayed it with Lemon Pledge, but it no longer keeps him out.

Any suggestions for deterrents?

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You can try something like Bitter Yuck or Grannick's bitter apple sprays, but of course I'm not sure that would be effective on something like a bathtub or shower since presumably those will be having water splashed about, probably washing that stuff away. I think you are confusing your poor cat, making me glad I didn't try to toilet train mine.

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The little monsters 3

I agree with Brian. The issue is the toilet training. Your cat associates anything resembling a toilet to use it as a toilet. This is why 99% of cat owners use a litter box. Toilet training is a lazy way out and cats are not familiar with that method. Your kitty associates the bathroom with doing his business. Outside of putting a cover over your tub (and he would probably go on top of that), you are not going to keep him out of your bathtub. Be thankful that he at least uses something that is easily cleaned up as we have members complaining their cat goes on their bed, on their laundry, etc.

The ONLY thing I can suggest (outside of getting him a litter box) is one of those motion-sensitive air canisters (you can buy them online). Put one in the bathrub and when he jumps in, it will spray air. That should scare him to get him back out. Hopefully, the canister would not go off when you enter the bathroom. I'm sure there may be settings on the can to adjust for that. Now you have something that will not harm your boy or your tub. And it is easily taken out if you want to take a bath.

You might try this product: PetSafe SSSCAT Deterrent Cat Spray

Google it and see where you can purchase it. It may use refills that you can order as well.

What happens when the cat gets old and possibly has arthritic issues, ect? If the cat can't balance right over the toilet due to age? What happens? Then they start doing their business in places you really don't want them to because they can't help it. :(

I would just litter box train him, it doesn't really sound like it is worth all this hassle and you may have issues years from now you didn't consider.

To make scooping easier, I got one of those baby diaper pales that trap smell. I scoop that poop into a dog poop bag, tie it off and put it in the diaper pale. It makes life easier when living in an apartment as I don't need to run to the outside garbage with every scoop.