"bury chicken-wire just under the surface of your flowerbeds; cats catch their claws in it when they go to cover up their doings, and they hate that"

By the time they are trying to cover up their doings it's too late, the deed is done.
The cats round here just seem to do it on the surface, with very little attempt to cover it - if I put anything down to discourage them they just do their doings in top - I'd rather just shovel it up than try to get it off chicken wire or twigs or whatever.

I used to have a little cat who went to great lengths to bury it - she would dig a deep hole as deep as her arm would reach, and afterwards fill the hole and keep covering and sniffing until there was no smell to give away where she had been.