Ways to prevent UTIs (Urinary Tract Infection) in older dogs?

My sister has an 11 year old German Shepherd mix. She has become prone to urinary tract infections in the last year. She has had two so far this year. The veterinarian said that they do get more common as a dog ages.

I was wondering if anyone else has dealt with this issue with their dog. Did you find anything that helped to prevent recurrences? Are their any supplements or special foods that might help?

It is no fun when a dog gets a UTI! My previous dog had two in her final year. She was miserable until the antibiotics started working.

Thanks for any suggestions!