I then use Really Right Stuff lever Quick Release clamps on the top of my tripod ballhead, fluid head, monopod, Zacuto, Sony monopod support system, and slider.
You can also use screw clamps, they will adapt to any RRS, Arca, Kirk, etc plate.
There is also a gut on eBay who sells 501 plates with an Arca type clamp mounted on the plate. I haven't used them, so I can't vouch for them.
I have used RRS for 15+ years after being totally frustrated trying to get Manfrotto plates to stay secure. RRS are really well engineered. Use a l;ittle non-permanent Loc-Tite and they stay put! Never, ever had an issue.