Denby is a Urological Surgeon who investigates and treats diseases of the male genitourinary tract and female urinary tract. He graduated from Adelaide University in 1982, trained in Adelaide and attained fellowship of the Royal Australasian College of Surgeons in Urology in 1991. He worked in London for a year and has been in Private Practice in North Adelaide and Calvary North Adelaide Hospital since 1993. He treats most urological conditions but has particular subspecialty interest and expertise in the minimally invasive treatment of prostate cancer with LDR (low dose rate) and HDR (high dose rate) brachytherapy and minimally invasive ureteroscopic and percutaneous laser kidney stone surgery.