Here, I keep a playlist I call "Hidden" tucked away in the the playlists tree somewhere. When I come across anything I don't want 'random' playback (including Play Doctor) to pick, I add it to that playlist. The right click, send to, playlist menu is good for this task.
Then, when building smartlists, or views, where I do not want those files appearing, I just add the playlist exclusion. It doesn't need the full playlist path, simply typing "-p=hidden" into one of the rule lines ensures that those tracks are excluded, though keep in mind that "Hidden" does not feature in any of my other playlist names. If it did, the path would be required else the others would also be excluded.
For me, this works best because by simply adding the track to the playlist, it is then automatically excluded from all smartlists and views that contain a rule the explicitly excludes that playlist.
It can be handy for things such as duplicate files. I have a few of those I like to keep so that albums are complete. Some are better quality than others and so on. So, the 'best' file stays off the hidden list, while all the others are on it. Random lists with the playlist exclusion rule will never play these files, but, if I go to my albums view and pick an album to play, the whole album will play, even if it contains tracks on the hidden list. I've used this approach for years and it works really well for me.
-marko