Using decoration pieces in marine tanks that are suited to freshwater tanks.

Many decoration pieces for freshwater tanks like sunken ships ands skulls to name only two, are not suited to use in saltwater due to leaching of chems from its make up.
Personally i do make many items to put in my tanks that could be toxic to my water, but what i do is cover the item with a resin.
An epoxy resin is the best of the best, but i find a the cheaper easier polyester resin works fine to seal in any and all potential toxic leaks. I get a spray bottle, general purpose thinners and mix the resin with the thinners to thin it down and thinners cleans resin off you as well, then mix in the catalyst/the hardener and place the item on some news then lift it up, you should be wearing gloves now as you spray your decoration piece.
Once all nooks and crannies are soaked with resin, then sit the item back on newspaper once the resin has been applied and direct a heat gun or hair drier at it to begin the hardening process and then leave in the sun till its not tacky/sticky anymore and the next day its ready for use!  
Oh and you can also add in some pigment/colour to your resin as well in many ways to make it look more interesting, of course just buy a cheap spray bottle from the supermarket or hardware store, its a one use thing for the spray bottle, its not worth rinsing it out with thinners to reuse it.