Not attaching to anything is a sign of stress. Provide it with pristine water conditions, more than ample light to feed the photosynthetic zooxanthellia that are absolutely necessary for it's survival. Do not overfeed your anemone and make sure that you have sufficient water flow. But you can't force it or coax it to attach to anything. Also be aware that the little pains will move where ever it wants, including into your prize patch of Zoas that you have lovingly tended to for months.