The material or compound could be in solution from where it could be electro-deposited onto a second surface but the deposited layer of material from solution becomes non-conducting after deposition.
As Qhatan above me suggested polymers is one good option since if you make a thick layer you can actually block the electrode at some point. Another option is something slimier to SAM's that can also block electron transfer to the electrode if they are long enough (for example C-10 and higher).
As Tomer and Qhatan suggested, you can use a class of polymers known as insulating polymers. For example, poly-m-phenylenediamine is a popular insulating polymer used in biosensors to block other molecules from reaching the surface.