Leave the anemone's foot alone...
From the pic, it appears the anemone has settled in the sand. I'm not 100% sure which type of anemone that is(a little help here), but a lot of them will not bury their foot in the sand or substrate. They just sit on top...
However - leave the foot alone, if you cut or tear the anemone's foot, it will usually die. Making a huge unwanted mess of your aquarium...