Jacco was reported to weigh 10 to 12 pounds (4.5 to 5.4 kg) and was pitched against dogs of up to twice his weight.
Lennox writes that after several fights, Jacco adapted his technique and would overcome his canine opponents by leaping directly on their backs and manoeuvring himself into a position where he could tear at their windpipes while remaining out of reach of their jaws.