Some more suggestions ..
1) Do you actually like the song ? I find it hard to remeber lyrics to a song that I'm less keen on.
I think what's happening is that when I like a song a lot, there are 'hooks' - just moments in the song which I look forward to. If I think the song is kind of ok but nothing special vocally (I have to like it a bit else why would I bother!), then these hooks may not be there and it's much more difficult to remeber the detail.
1) So another trick might be to invent some parts that you like ! I don't necessarily mean change the song, just try and find a part in each verse that you'll enjoy or which sticks out for you.
2) Make a point of learning, as a lyric in itself, the end of one part and the start of another so you can more easily remeber how the song fits together.
3) Remember the "audio" of how the song sounds- ie listen to it a lot. Get it embedded into your brain.. then if you forget the lyrics you've got something to call on. Watch out- this might drive you nuts haha
4) UNderstand gist of the story behind the song. This may not help with the song you quote if it's a bit meaningless to you, but sometimes a song tells a story and remebering the story helps trigger which bit goes where.
5) Play it ! writing the song down definitely helps, as others suggest, but when it comes to finding the words right there and then, a bit of entrenched memory will help, especially re timing and reference to how far it feels like you are through the song.
6) Last resort : Queue cards. Maybe just the first word/phrase of each part. I know a few vocalists who do this. It can look naff, but it works and eventually you won't need the paperwork.
I hope this helps. Note that you're not alone! remebering lyrics can be pretty tricky