As there is no really successful method for preventing the slow but inevitable compaction of the sand within a sand box .its efficacy will slowly deteriorate to become virtually zero.
Interesting info Henry - in a grim reaper sort of way :^(
Annual sandbox maintenance - once a year.
Difficulty level - 2 out of 10.
Procedure.
With a buddies help remove TT with shelf from the sand.
Remove sand with scooper and place into a secondary container (bucket)
Carefully check sand when removing to determine if audiophile cat has used it over the course of the year.
Pour sand back into box. Install shelf and TT back into sand.
Level as required.
Time required. One hour depending on whether sand was soiled.
Does this suffice ?
I am curious how often the air suspension shelves (i.e. vibraplane) need re-levelling from bladders losing air. Especially any bought used on the internet ?