The Ohio State University has expanded its wonderful Indoor Cat site to include dogs. The importance of mental health to overall health and well-being has long been identified in human medicine. Poor welfare and chronic stress can also lead to mental and physical health problems in our pets.
The treasure trove of hints and help for keeping indoor cats is still there - just click on the pic of the cute kitten on the left. I've found the problem solving section especially useful for stressed pusses.
The Indoor Pet Initiative