get some korda dark matter tubing sinks like a stone and much safer than leadcore if you want to fish a chod rig get some naked chod beads and rig them up on your mainline you can always dot it down with blobs of tungsten putty but if you use fluorocarbon mainline theres no need for the putty.
if you want to just get your mainline on the deck spend some time paying off line until it sinks and lays tight to the bottom before setting your bobbin.
hope this helps.
clive.
i prefer not to use leaders with loops and just thread my mainline through the tubing and then tie to my lead clip or through a inline lead its much safer for the fish should you snap off.
the tubing also goes someway to protecting the fishes flanks and helps prevent lifting scales during the fight.
good luck with your fishing
clive.