Well, I am happy to report that although the 'Watch your doodoo!" continues, he has now learned to say "Be caaaarefuuul!" This is something that I say to them when I am in the process of making two birds like (tolerate?) one another. There is usually one that is the 'attacker' so, whenever I see this bird approaching the milder ones, I say "Be caaaaaarefuuul!" The funny thing is that, although originally it was meant for the milder one (the phrase for the attacker been "I'm watching you!"), now both birds pay attention to the warning with the attacker understanding it means he (actually, it's usually a 'she', Zoey) is supposed to stop and the mild one understanding that he/she is to be on his/her guard.
This morning, I was doing the canaries with my usual peanut gallery: Zoey, Isis, Sweetpea and Codee (Codee on my chest, as usual, and the other three either perching on me or on the cages watching what I do) when I see Zoey flying over to the top of a cage where Sweetpea was and landing VERY close to him so Sweetpea says: "Be caaaarefuul!" I almost fall from the little stepladder I use to reach the top shelves laughing!