I hav one that requires litter changes weekly. That seems to keep her
from ****ing on the wall, instead of in the tray. A time wuz when she
would tolerate every other week, and she would politely indicate when
she could smell it: She would **** in the bathtub, instead. I use plain
clay. I haven't tested whether this cat would prefer silica or wood
chips. I would never use the clumping stuff; too much maintenance for me.

All I can think of doing is increasing the frequency of litter changes.