Get roses with glossy leaves, they do better with blackspot. If it rains a lot there isn't much you can do without a regular fungicide program. If you know rain is coming you can start a preventive program using either sulfur or an oil but you have to choose one since they cannot be used within a month of each other. Space the roses so they have very good air circulation and prune them into a vase shape. They should be pruned and fed after each bloom cycle. If you do have blackspot you will need to pick up all of the damaged leaves and destroy them to keep the spores down.