Just wanted to pop in -
Our beagle had a few recurrent UTI's and struvite crystals over the course of a few months, I had them culture her urine. We treated and fed the RX food as we were told to. She seemed to get better, the UTI's went away - then maybe a year or so later, she out of the blue pee'd herself just standing there (the only symptom she ever had with UTI's as well - spontaneous peeing) but this time it had spikey stones in it.
I of course called the vet, got an appointment for the next day and by that first evening she was leaking bloody urine all over the house. Prior to that she had no other symptoms - no straining, no excess thirst, no frequent urination, etc.
At this point we had switched vets, and were told that A) her stones had likely been forming for a long while and B) a lot of dogs with stones present with other symptoms unrelated to the stones and that's when stones are found - they often don't have accompanying symptoms until it's bad. Also that, depending on the type of stones they can be dissolved through diet - but for her it was too late.
She was 80-90% blocked with stones, one as large as a golf ball. She was put on meds to treat infection and in surgery a few days later. $4000 later and a very sore puppy, it was over.
The only symptom she ever had, looking back was that her stomach was always sensitive if pushed on in a certain way - she likes to stand over our feet when she wants attention and sometimes DF will lift her back end up with his legs under her tummy - she'd yelp if he did that. But she's very vocal and whiney in general, so we assumed she just didn't like it or that it was because she has a bit of hip dysplasia - this started way before the UTI's did. Since her surgery, it doesn't bother her anymore and she actually bugs DF to do it all the time
From now on, we will ALWAYS have an x-ray done the second a UTI or crystals are found in any of our dogs urine. Just to be safe.