You might however try to take advantage of a popular Trap in the Petroff Defense that favors White if you feel your opponent is just copying moves! ;-)
Ruy Lopez Question About The E Pawn

Why not just take on e5 with the knight? If black takes on e4 it's just a trade. Or you do what e4forme said. I think taking on e5 is less passive than trying to protect the pawn
But then again, I'm overly aggressive...
About playing the ruy lopez thing, keep in mind that sometimes you NEED to adjust your opening settings depending on what the opponent does. There is no opening that's going to work for every response.

If Black insists on playing the Petroff or Russian Defense with 2.... Nf6, you can try to transpose back into the Ruy Lopez with 3. Nc3. If Black answers with 3.... Nc6 (The 4 Knights Game), then you can get back to the Ruy with 4.Bb5.
You might however try to take advantage of a popular Trap in the Petroff Defense that favors White if you feel your opponent is just copying moves! ;-)
NO.
In a 4-Knights, Bb5 is a "Spanish Four Knights" (as opposed to d4, leading to a "Scotch Four Knights"). It plays very differently from the regular Ruy, in that very seldom does White play Nc3 (c3 & d4 often are paired up to attack the center or allow the Bishop to retreat to c2) and the Rubinstein move against the Spanish 4 Knights (Nd4) is not exactly like the Ruy's (very unpopular) Bird Variation 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nd4.
Furthermore, if White plays 3.Nc3 from an attempt at the Petroff, Black often plays Bb4 himself, allowing Nxe5 but getting a lead in useful development with 0-0 and expanding int he center. I lost the only time this was played against me. Transpositions are a dangerous game.
The main thing you need to learn is that you, as white, cannot "decide" which opening to play. You may intend to play the Ruy Lopez, but Black has some say in the matter too! If Black chooses not to play 2...Nc6 then you aren't playing the Ruy. Black's choice of 2...Nf6 is called the "Petroff Defense" or "The Russian Game." and it's perfectly respectable. As several people have suggested, 3.Nxe5 is the main move.

The main thing you need to learn is that you, as white, cannot "decide" which opening to play. You may intend to play the Ruy Lopez, but Black has some say in the matter too! If Black chooses not to play 2...Nc6 then you aren't playing the Ruy. Black's choice of 2...Nf6 is called the "Petroff Defense" or "The Russian Game." and it's perfectly respectable. As several people have suggested, 3.Nxe5 is the main move.
Yes! For years before there were books on the subject and world championship contenders played it, I used to play 1.e4 c5 2. Nf3 Nc6 3.Bb5 and say to my opponent (in casual games) "I'm playing the Ruy Lopez, what are you doing?"
Thanks,
Mitch