My dog has a cough

Rita is almost 14, gets lots of exercise and seems extremely healthy, especially for an old dog. She has developed a cough that seems the worst when she has been lying down for 2-3 hours. When I exercise her, the cough goes away until she rests or sleeps for a while. She does not seem sick at all. Sometimes she coughs up a little foamy saliva. She gags a little at the end of a cough , like she is trying to cough something up. She had a cough like this a few months ago, and it went away on it's own, but this one is not going away. Any ideas? My vet died a couple of years ago, and I have yet to find anyone I like, I will take her to someone if it persists, but I was hoping someone here could help me.

In an older dog it can be any number of things: lung disease, heart disease, the beginnings of a respiratory infection, etc. A vet check would be advisable, plus you really should have a vet in case of a true emergency, so this could be an easy way to start a relationship with a new clinic!