Apparatus for occluding a space between a first structure and a second structure, said apparatus comprising: an occluder, said occluder comprising a distal implant and a proximal implant, wherein: said distal implant comprises a body and a locking shaft mounted to said body, wherein said body of said distal implant comprises a plurality of legs which may assume (i) a diametrically-reduced configuration for disposition within the lumen of a tube, and (ii) a diametrically-expanded configuration for disposition against the first structure, and further wherein said locking shaft comprises a first locking element for selective connection to said proximal implant and a second locking element for selective connection to an inserter for deploying said occluder; and said proximal implant comprises a body having an opening, wherein said body of said proximal implant comprises a plurality of legs which may assume (i) a diametrically-reduced configuration for disposition within the lumen of a tube, and (ii) a diametrically-expanded configuration for disposition against the second structure, and further wherein said body of said proximal implant comprises a third locking element for selective connection to said first locking element of said distal implant; wherein said locking shaft of said distal implant is slidably receivable within said opening in said body of said proximal implant, and further wherein said first locking element of said distal implant and said third locking element of said proximal implant are selectively engagable with one another so as to hold said distal implant and said proximal implant in fixed position relative to one another.