HELP ! Litter box harrassment! LOL

recently our kitten Gizmo has been harrassing our older cat <1 & 1/2 years > Cynni while she is in the litter box... Gizmo < 3 months > will charge at her while she is trying to do her buisiness and she jumps out of the box in fear.

How do I discipline him, so that he doesnt become fearful of the litter box. If my husband keeps picking him up saying NO, he may think/learn he is not allowed to use the litter box?

Any help appreciated.

my kitten named socks is also three months old. He always messed around with Birdie/3 year old when she in the cat litter box. we bought a water gun. we sprayed him when he is going to attack birdie. Now he knows not to mess
around with birdie or big sister.

Is it a covered litterbox?
If not, maybe one would help.