There's an easier way to solve this.
See, there's nothing special about that answer that makes it a target for spam - there are plenty of other answers that get attacked on a regular basis.
However, the system doesn't silently discard spam edits for that answer, even though it does for lots of similar edits elsewhere. Why? Because that answer is very short!
The system is stupid: it can't tell the difference between someone making a few minor spelling corrections across a few sentences and someone replacing those same handful of words with outright spam. For reasonably-long answers - over 400 characters by default - it just assumes that anyone replacing the entire post is up to no good and quietly throws the edit away... But for very short answers, it doesn't do this. And so you get persistent spam on short answers.
We're working on systems that are a bit smarter, which should reduce the problem here considerably. In the mean time, don't worry about putting special tags on the question - just flesh out the answer a little bit and the problem will go away. I've done this by just adding an image and a description to go with it.