When Roughhousing Becomes Too Rough

Q: I have two dogs, a 9-month-old pit bull mix and a 13-month-old lemon Dalmatian. When it comes to playing and toys, the Dal is very submissive and the pit bull is aggressive. I have had to break up their playing because the Dal will not let the pit know when she is getting hurt. I have since found about half a dozen scratch marks on the Dal's neck from the pit bull. How do I curb this type of behavior? I'm trying to find a way to allow me to keep both dogs, but so far have been unsuccessful.