How to cat-proof apartment ledges without permanent changes

What people tried

Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.

1. 1
   leaving the ledge unproofed and trusting the cat's balance
2. 2
   wrapping the ledge top with aluminum foil as a deterrent
3. 3
   removing items like vases and lamps from the ledge to prevent them from being knocked over
4. 4
   Using bird spikes across the ledge
5. 5
   Placing soft items like cushions or an armchair in the fall zone
6. 6
   Adding grips to surfaces or edges
7. 7
   Installing a net, chicken wire, or glass wall

In their words

Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.