Not that i have immediate plans for this knowledge but I've been reading all over about agar work and one bizare thing I came across was utilizing envenomated agar! That is, adding a percentage of powdered snake venom to your agar mix to help with the sprouting of hard to sprout seeds/spores and making invitro mushroom mycelium hybrids by the venom weakening the cell walls of whatever is placed on it but I assume it's easy to overdo it and kill the culture.
Unfortunately no ratios were given as to how much is used in a liter of agar solution. Sigma chemical sells a variety of powdered snake venoms but in microgram increments, it ain't cheap, so I assume not much is required.
How about adding powdered activated carbon in your agar to get fewer contaminations? Phyto Tek Labs even sells orchid agar mixes with activated carbon already added, is it worth it? Of course you must use sterile technique with agar but any extra preventitive is a plus in my book.