"Congress can stop the fence down the line in many different ways; cutting funding and without a line item veto it would work, tie it up in countless committee hearings, etc. Give Democrats control of the House or Senate in November and the fence will be dead."
The fence has already been passed by both branches and finded. The only way that any of the ways you stated above would work is if the President vetoes it, and he has said he will sign it.
That leaves only one option. The Dems have to win at least the house or the Senate and create new legislation to stop the fence, then get that new legislation to pass in both houses and get the President to sign it, or get enough votes in both houses to override a Presidential veto.
I learned a long time ago, it's not wise to underestimate Congress, particularly the Democrats. If they gain control over either house I put nothing past them.