According to the most recent scholarly article I can find on the subject, no one knows what causes this disease yet. Specifically:
[cutaneous and renal glomerular vasculopathy (CRGV) aka 'Alabama Rot'] is a disease of unknown aetiology carrying a poor prognosis when
Vet Rec. 2015 Apr 11;176(15):384. doi: 10.1136/vr.102892. Epub 2015 Mar 23.
Cutaneous and renal glomerular vasculopathy as a cause of acute kidney injury in dogs in the UK.
Holm LP1, Hawkins I2, Robin C3, Newton RJ3, Jepson R4, Stanzani G4, McMahon LA1, Pesavento P5, Carr T6, Cogan T7, Couto CG8, Cianciolo R9, Walker DJ1.
The only preventative measure that I could find suggested was that you wash your dog after each walk, but there's no evidence that washing helps (and dogs that have been washed have also become ill).
Essentially, until they are able to figure out what causes it, there will not be any good recommendations on how to avoid the disease. The best advice I found suggested that if your dog develops any sores or wounds, you should go immediately to the vet for advice. Dogs who are not given supportive therapy for their kidneys quickly tend to have worse outcomes than dogs who are treated promptly.