I've used silicon and slate before but gave up because I kept pulling them apart when takin them out for maintenance. After about 6 months mine sinks, barely (damn you cedar!)
I still put rocks on it to keep the filter from blowing them around.
If I did it again, I'd attach them to a piece of slate with a high quality stainless steel screw.
Blacksmith, no offence, but IMO you're
Lead is nasty stuff.
If lead contacts acidic water it leeches fairly quickly (so I was told, same with copper.)
Not to mention my kids health is worth many time the couple of bucks it costs for stainless steel to keep lead completely out of my house.
Iron, and most metals are toxic to fish when in excess and even if the fish live, iron can contribute to algae blooms.
If it's not safe for humans and you give a crap about your fish, don't risk it.