Salt water in general is a bad idea. It can corrode over time and depending on the setting, the first thing to become damaged are the spokes that hold the gemstone in place. It can also effect the gemstone.
Yes, odds are it's not going to fall to pieces the first time you do this, however, I wouldn't suggest messing with the possibilities especially when dealing with your future wife's ring ;)
The links provided discuss not only the effect salt water and chlorine have on jewelry, but also make suggestions for cleaning.
The use of a very little bit of ammonia is excellent. Ammonia is used in hoodoo as a purifier and cleanser so if you want to dip the ring in a liquid solution, that would give spiritual cleansing as well as make it look pretty.
You can also smudge the ring, which would eliminate the need to get liquid on it at all.