Although I think it is great to give cats an outdoor experience by taking them out on a harness, I am not in favor of letting kitties roam freely inside and out, especially when I am looking after them.
As a professional pet sitter my number one goal is the animal's safety. For that reason I do not sit for cats who are permitted outdoor access when I am caring for them. The reason is that most of my kitty visits are for a half hour once a day. I need to see the cat during that half hour and know that he/she is doing well. If they are out and about roaming the neighborhood I have no idea if they are safe or healthy and am unable to report their well-being to their pet parent.That just doesn't work for me.
All of my clients understand this but apparently some of the cats do not.
On two separate occasions, with two different cats, I have gone to do my kitty visit and have been unable to find the cat. I know some cats hide and always do a thorough search to be able to eyeball them and know they are okay. After searching everywhere, I still did not see the cats. Then I did. Outside. One was playing in the bushes ; the other I found standing on his outdoor patio looking to come in. After securing the cats in their respective apartments again, I made an effort to find out how they had escaped in the first place. In both instances, they had made a hole in a screen window and squeezed through. Needless to say, I closed the glass windows and informed the pet parents of what had happened.
Kitties are smart, and where there is a will, there is a way; however, my motto is always Not On My Watch!