There would be no way to know for sure.
However, that would only be an issue IF our congressmen were currently representing us.
Would you rather your congressman answer only to his conscience and HOPE that he represents your interests or answer to others and KNOW for certain that he does not represent you?
Think of it this way...If he tells his constituents he is pro-life, anti-federal power, anti-illegal immigration or some other position, what would be a reason for betraying them when it was time to vote? Currently they say all of these things yet they vote to fund Obamacare, expand federal power, fund Obama's amnesty, etc.... We all know why they say one thing and do another. Why not get rid of those motivations?
The thought occurs to me that Washington DC, being an evil cesspool, will work out a way to ascertain the manner in which Representatives are voting, regardless of what we do. We might be the only people who end up not knowing how they voted.