iPod smart playlists and autosync

I've created a smart playlist for my daily workout. But when I plug my iPod in after my workout, iTunes immediately builds a new playlist overwriting the current one. Is there a way to avoid this? I want to tell it when to rebuild the smart playlist (by manually deleting the songs from the playlist and having it build a new one). Also, about 1 in 10 times I'll turn my iPod on and my workout playlist will be nothing close to what I had just created in iTunes. Sometimes it'll be just a few songs of the iTunes playlist and other times it's been so far off it's songs I didn't even remember I had in my library.

Long story short, I want to have a smart playlist based on the criteria I've selected and never have iTunes change it unless I specifically tell it to. Possible

Thanks for your response. That's unfortunate if it's truly the default behavior. I used to manually manage my music, but then I would end up with duplicates when a song was part of a playlist and an album. Can't win either way, I guess!