I personally like Deb's Website since on the page that lists each restaraunt it tells the last time the menu was updated on the site. Several things to keep in mind.
1. Counter Service restaurants change very infrequently. The only exception is that if they rethink the "concept" then it can be a wholesale change.
2. Fine dining will have a few signature items that are always on the menu. The rest of the entrees may gradually change but will keep in the "theme" of the restaurant. Appetizers/soups may change more often.
3. While not as prevalent, make note of any chefs changing venues. A few years back, the head Chef at any particular restaurant were more publicized, now they are more in the background.
In summary, if you like the overall recent menu as seen on the web, for a particular restaurant, you should like it when you go.