About your post Furion. I find that when they move to Salona they can cross at the bridge just north of Sirmium. A fort just across the bridge usually discourages them but park your army on the bridge. (It doesnt have to be that good as the garrison can help you.) They also cross at the passes near Salona so put forts there and you should be completely safe from incursions and have an army that can help for any that slip through