*WAY OFF TOPIC*
Dude! Your avatar is Chopin! Sorry. I just love Classical Music.
*Back to topic*
You're actually the only person to point that out (or probably even notice haha)
*High five*
Anyways, having a strategy that revolves around breaking someone's shield is a waste of time. It's similar to a strategy of helping Ness recover health or filling GW's bucket. Smart teams can easily exploit it. A broken shield is really not that high of a reward. One free hit. If you're using two people to focus on breaking one person's shield, the other person will be there to save them once the shield is broken. If it's two against one, a simple grab is much more efficient. In all the time it takes you to maybe break someone's shield, Snake can just ftilt to rake up damage sooo easily.
Common sense -- you just have to play smarter than the opponent.
You, as Marth, are a much better edgeguarder and aerial fighter. You should be the aggressive one while Snake has your back. Sword dance is also a great team move. It soaks up time. Go for the downb as the final hit of sword dance so that Snake has time to react and come hit them out of it.
Make sure Snake keeps his main kill moves fresh. Even against smart opponents, in doubles it is much easier for Snake to get kills with utilt and the C4.
Practice a lot with each other, even against computers if you have to. Experience forges good communication and teamwork. When you two are working in unison, you will dominate the air while Snake controls the ground. Go for the gimps when you can. Snake will get the easy K.O.'s.
A simple code language really isn't hard to develop. If you're not smart enough to develop one, then you're not smart enough to win
Another thing I forgot to mention earlier: when your partner Snake is cyphering, jump on it. It won't footstool them down, but it still technically counts as a footstool. So basically, it doesn't affected them in anyway except for giving them another cypher. Not that practical, but helpful to know.