If your tripod head is not compatible with Peak Design Products, fret not. For less than $30 you can turn almost any tripod ball-head into an Arca-compatible head (and thereby a PD-compatible head). Here's what you do:
1. Buy an ARCA-compatible clamp.
If you're price conscious, you can get an Desmond clamping with RC2 Adapter head off Amazon for under $30. Make sure you get a knob-release clamp and not a lever release clamp.
2. Remove your tripod clamp and install the ARCA-compatible clamp.
Most pro-quality tripod heads (like those made by Manfrotto®) have a screw that allows you to remove the clamp portion of the head. Undo this screw to remove the old head, and use the same screw to install the ARCA-compatible head. This video walks you through the process:
3. Alternatively screw the clamping head atop your 3/8" tripod head or 1/4" tripod screw.
If you don't want to remove your old tripod clamp (or can't), use this option. Lock your old quick-release plate into your tripod. Then attach the ARCA-compatible clamp to the quick-release plate. The Desmond head has a spacer that allows you to put it on either type of tripod mount.
That's it, you're good to go!