Simple but fairly effective liquid formulas could be a base of either bobcat urine or fish oil with a few pulverized cat glands, ground castor and a dash of skunk musk. If you want to get more elaborate, generally the more ingredients a lure contains the more effective the lure gets and cats like musky smelling lures. Tonquin musk, civet musk, musk ambrette and muskrat musk are good additions but don't use so much skunk musk in the formula that the excellent milder ingredients get overpowered and nullified. Catnip is good too and can be a real asset when used in the correct amount but don't overdo catnip as too much can actually repel cats. Don't forget to add a little sodium benzoate to preserve the lure and some glycerine to keep it from freezing. Good luck! Ace :-)