Hi,
I remembered when i saw this one episode of 'my cat from hell' ( i couldnt remember the exact episode) , where jackson galaxy gives a tip to avoid the cat aka the client from jumping over the fence. ( so, a balcony may apply too perhaps?).. He said to install a 45 degree fence. Naturally, cats will avoid jumping over it. Maybe not a fence la but maybe you can find sumthing smaller n similar to fit the balcony. You get the idea right? It is something like in the picture. It is also called as the deterrence fence.
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Hope this helps.