I think I've answered this questuon before but here it is again. Select a stray vertex. Open the component editor and go to the tab marked skin clusters (Joint Clusters are for Rigid Bind, same concept as well) In the component editor it will show all of your joints with numbers below them. Depending on how many influences you had set when binding, let's say 3, you'll see numbers under each joint that influences that vertex. the sum of the numbers in a row will always equal 1 so find the joint you don't want to influence the vertex and assign a value of zero, the remaining joints will reflect these changes to equal 1.
Furthermore you can also use the prune small weights under the edit smooth skin option. This tool lets you set a value of say .1 that will get rid of any stray weights that are being assigned to weird joints. I had a character that I had skinned and for some reason some of the verts on his chest and back were skinned to his knee, but pruning the weights fixed it.
sorry it's so long but I wanted to make sure you got the concept, and I don't know how experienced you are.
Hope this helps.
Cheers!
