Jane et al: I have heard that there are some rodenticides that don't allow secondary poisoning such as was described in the death of the borzoi. I think it may be zinc phosphide that reacts with the acid in the gastrointestinal tract and releases a gas that poisons the rodent. The gas does its thing and then moves on and secondary poisoning is not a problem. Of course I would be hesitant about this until I had researched it a bit more. I will do a bit of looking and report back Arnold New Jersey