Maybe we should go back to the question asked at first by 1stupidpunk, who is by the way, a good, knowledgeable hobbyist. "Why do you want to contain this anemone?" Are you aware that anemones are escape artists? Have you noticed that they are changelings? Huge anemones can squeeze though a hole the size of a small pea and between slits on powerhead screens. They will roam all over to find the right spot where flow and light are just right. They need to breathe, eat and excrete. They will suffocate if they cannot get enough water flow for those three purposes. A container restricts water flow, hindering their ability to respire and eat and leaving them to wallow in their excrement. Have you ever seen an anemone or coral succumb to these poor conditions? You may have but you may not have known that was happening.

When I want an anemone to stay put for a while, I find a small fist size rock it likes and then place the rock on the open sand away from the main rock structure where it can't migrate and become difficult to remove. I place it where the water is flowing smooth and swift but not too fast. I watch the anemone response for an hour or so for tentacle hydration, which means it's happy. If it's not happy in a spot, I move the rock over the sand to a new spot. An anemone may often like the leeward side of the rock where the water current forms eddies. The anemone usually stays put for days or weeks, until its time for it to go to a new home.