Another option - I had a balcony that I was going to secure and was considering using balcony netting (like this https://www.amazon.com/gp/product/B01LY8W0LN/ref=ox_sc_saved_title_10?smid=ATVPDKIKX0DER&psc=1). We moved so I never did it (and the cat really didn’t like the noisy city balcony anyway) but I noticed that others in my building had used a similar product on their balconies.