There is no effective fungicide for artillery fungus, nor any kind of sealer that we've heard of.  Generally, your best bet is to remove the mulch that has the spores.  Don't reuse it elsewhere unless it is far from anything problematic, such as a shed or lawn furniture.  Possibly throw it in a woods. You can also bag it and send it to the landfill. Replace with fresh mulch or groundcover.

Here is more thorough information: http://extension.psu.edu/pests/plant-diseases/artillery-fungus/faqs

 ECN