I have cross bred a female Skarmory, with a male Altaria, so the baby Skarmory, was born with the moves:
Leer, Peck and SKY ATTACK.
Sky Attack was the move Altaria knew.
I put the baby Skarmory in Day-Care, knowing that sooner or later the move will be overwritten by a new move.
So I went out and stole a heart scale from a Wild Luvdisc.
So I could re-teach the move when I go to the move-tutor.
Later, I took out my baby Sakrmaory and sure enough it had forgotton Sky Attack.
So I went to the Move-Tutor to ask for a re-teach, and he couldn't teach baby Skarmory Sky Attack, presumably because it was unnatural to him because he was a cross breed.
I still have the adult Skarmory and Altaria, so I can continue making eggs, but I don't want to teach him up to level 45. (Which is when he learns his last move, Metal Sound.) So is there any way I can protect a move from being overwritten, or at least ALL of the moves to be protected from over writing.