Items in Common Areas

[Makan A Tabrizi]

I'm trying to update my lease for a 5 unit in Colorado. I'm currently allowing tenants to use their own lawnchairs in common areas. I've never had any issues with this but a thought occurred today. What if another tenant is using the same lawnchairs and has an accident? Technically they are placing the items in common areas with my approval. I'm guessing I'm accepting liability because I allowed this to happen? How can I address this in the lease to reduce my liability? 

This could apply to anything left in the common areas by one tenant that might potentially injure another tenant. I could make a blanket clause that says nothing, including bicycles, is to be stored in common areas but I want to make the place more welcoming and personal.

Thanks in advance for your input.