I have rarely had dogs with a UTI, and all just once. But I have friends who have dogs who kept getting and developed stones/crystals etc. So I agree, they need to figure out why.
From UC Davis http://www.vetmed.ucdavis.edu/ucvmc_sd/nephrology_urology_hemodialysis/services.cfm#lower
Chronic urinary tract infections
Urinary tract infections (UTI) are usually bacterial in origin and can affect either the lower urinary tract or both the upper and lower tracts. Bacteria from the intestinal tract and the external genital region ascend through the urethra into the bladder on a regular basis; the balance between bacterial virulence factors and host immune defenses determines whether the bacteria can colonize the bladder and cause UTI. Some concomitant patient factors such as kidney failure, diabetes mellitus, Cushing's syndrome, urolithiasis, hyperthyroidism, the presence of a urinary catheter, incontinence and spinal cord disease, among others, can increase the likelihood of UTI. Sometimes medical situations such as the ones listed above render the infection more difficult to clear and may make a pet more likely to become reinfected. Medications that suppress the immune system can also increase the likelihood of developing UTI and/or complicate UTI treatment. When patients develop sequential UTIs, have difficulty clearing a UTI despite appropriate management, systematic evaluation of patient anatomy and physiology may help to identify complicating factors and appropriate methods for clearing/controlling UTI.<<
Some basic ideas such as washing area to decrease bacteria, more fluids to keep flushed, etc:
And from beloved vet Wendy… stricture issue? There is a lot more to article but that part below. ALSO, you can contact them. Wendy walks on water as far as I am concerned... ask her for ideas.
Sometimes when an infection simply cannot seem to be cleared up, the reason is a vaginal stricture. A vaginal stricture is a small narrowing in the vagina, creating a ledge for bacteria to colonize. If a female dog's UTI seems stubborn against antibiotics that the culture indicates should be effective, a vaginal exam may be warranted. A stricture can generally be broken down by the veterinarian's finger though some dogs find this painful and sedation may be needed.