HI
Cat run in my opinion are very very good things, you need to make sure they are totally escape proof and if you feel you perhaps live in a dodgy area or would be worried about neighbours gaining access to your cats then you fit some sort of lock but apart from that its a way for cats to get outside, get fresh air, take excercise but be totally safe at the same time. It has certainly worked for me for many years now. You could have a plain run or one which combines some sort of housing/shelter. This can be totally independant of the property or if you are lucky you may be able to attach it to the house where the cats can come and go inside or out by way of a catflap.
I had to take down our very large run which was delapitated and no longer escape proof and we replaced it with a smaller and far less exciting one since our property is also on the market we just went for a bare minimum for them to get outdoor access but you can really make it fufulling with walkways , big branches/tree trunks etc.
I am lucky, our cats can come and go through a catflap, down a wee ramp directly into the cat run, then from this they can pass through another catflap entering their "cat shed" , pic enclosed sorta gives you the idea , it wasnt finished at this point (hubby was in the shed about to cut hole for that flap)
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