You say it by letting her feel safe in your arms and in your presence. By guiding her gracefully by a hand on her lower back and making sure she’s always out of harm’s way while you’re walking together. By giving her the attention she deserves and by demanding that same attention in return. By being there when she needs you, emotionally, physically, and mentally, and making sure she feels treasured and desired.
You say it by listening by taking what you learn and engaging her with that knowledge. You say it by owning her sexually and making sure she’s not only satisfied with your play together but simply overwhelmed by your shared passion for one another. You can say it with a collar. You can say it with a kiss. You can say it without saying it if you know how to make her feel it down to her naked essence.
If you want to say, “You’re mine,” and have her believe it. Then you need to make the words real and make sure she feels like she’s yours and feels safe in the sanctuary of the dynamic you’ve created together. If you’re going to say, “You’re mine,” then you’ll need to honor those words and hold her accountable to such a privileged distinction as well.