Although it may vary from region to region, the following breeds are considered to be potentially dangerous in Spain. Still, you can get them covered for an additional small amount per month.
Akita Inu
American Akita
American Bandogge Mastiff
American Bully
American PitBull Terrier
American Staffordshire Terrier
Boxer
Bullterrier
Bullmastiff
Doberman
Dogo argentino
Dogue de Bordeaux
Fila Brasileiro
Mastino Napoletano
Perro de presa canario
Perro de presa mallorquin
Pitbull-Terrier
Rottweiler
Staffordshire Bullterrier
Tibetan Mastiff
Tosa Inu
Cross-breeds of any of the above