A copyright holder has the exclusive rights to reproduce and to publicly display his work. So if you transcribed a composition and put it in your front yard, that could be an infringement of the copyright.
It would not be infringement if it were fair use, though. A fair use determination requires consideration of four factors:
the purpose and character of the copying: Your work is a memorial and arguably a work of art in and of itself. It is not commercial, but nor is it for the benefit of the public. It's not for entertainment, but nor is it for education. I'd say this is is sort of a draw.
the nature of the copied work: The copied work is a highly creative work at the heart of the purposes of copyright law. This factor cuts strongly against a finding of fair use, but it is the least important factor.
the substantiality of the copying: You're taking two stanzas; depending on the length of the song, that could mean different things. Two stanzas of "Supper's Ready" might not be that much, but two stanzas of "Find the Cost of Freedom" is the whole thing. I can't really say how this one shakes out.
the effect of the copying on the potential market: This requires a consideration of what would happen to the market for the composition as a result of your copying, but also of what would happen if your form of copying were widely adopted. Your personal use probably won't have much effect, but if people were generally permitted to plaster compositions all over anything they wanted, that would probably diminish the artist's ability to market his work.
So I'd say that we don't really have quite enough facts to assess whether something like this would be an infringement or fair use. As stupid as it sounds, it might honestly depend on whether the lyrics were facing the street, where any passerby could see them, or facing the house, where only you, family, and guests would see them. If they aren't displayed to the public, the effect on the market would be drastically reduced, which would go a long way in a fair-use analysis.
If it's not fair use, though, you could play it safe by getting a license. You'd probably need both a print license to allow you to create a visual depiction of the work, and then a license to publicly display the copy you've created. I believe both licenses would come from the publisher of the song.