There are a number of reasons for a BTA moving - not just it's foot. Ignoring any, or just not thinking critically about the animals in our tanks has lead to the myth that all nems move, and can do so with some frequency.
Here's my thoughts on the matter of wandering BTA's:
On the topic of a BTA moving "all the time" as some say...I would argue strongly against this statement. In my experience, from reading, and discussions with other people with far more expertise than me, a BTA will remain in its spot if all of its living conditions are being met satisfactorily. There is no benefit to the anemone (risk of being stung/sliced by corals, risk of not finding another rock in the ocean, predatory animals, etc) to "just move around" IF all conditions are appropriate.
Water quality, light, food, Flow, foot, and mechanical - the six conditions that must be satisfactorily met for all anemones.
Water quality: In the ocean, if local currents drastically change after storms, rivers dump crap into the ocean etc, the nem may want to move to conditions which better suit its liking. Other season factors can lead to different currents bringing a change in water quality to the anemone. In our tanks, however, there are no other areas which have better water - but the anemone doesn't know that. This is my #1 pick for why anemones move without apparent reason. It may even be something in your water which you do not test for - or it may be BECAUSE you just did a water change and didn't match tank water close enough. The anemone is searching for something it just can not find inside a glass box, hence the so called "anemone's just sometimes walk around for no reason". We can't see the reason - so we assume there isn't one.
Light: Lighting in the ocean is quite strong. Far more than our little electrical lights we use. Even on a cloudy day the par is very high - ever had a sunburn on a cloudy day? When you introduce a BTA, you may have a spot picked out that you really want it to go, but it may decide it is too bright or too dim and promptly move. Sometimes the holding facility will have very high powered lights, more often qub-optimal lighting. Make sure you know the conditions it came from, and acclimate as necessary to your tank. As it gets light-acclimated to your tank, it may move to a spot that is "just right" for its health in the long term. This acclimating and moving to a new home may also cause confusion to BTA's "moving a lot".
Food: Yikes! There are a lot of misconceptions about the "proper" diet for anemones. I did a write-up on RC a while back about the topic:
http://www.reefcentral.com/forums/showthread.php?t=1835320 A basic summary of that thread is.....assuming a healthy nem, food is likely unnecessary. If you would like to feed, feed small (pencil eraser max) meaty, raw, SW-found foods. Unhealthy nems need more food to gain energy and should be fed more. Feeding leads to faster growth. Feeding can also in some cases overcome less-than-ideal lighting because the food energy is supplementing the light source. More in-depth information can be found at that link.
Flow: You need to determine the flow requirements of the species of nem you want, and make it match in order to decrease the likelihood of movement. BTA's will like moderate flow, but not too high or too low. Either of those may cause it to move around. Some can be very picky. I know someone who's Haddoni moved across the sandbed after her cleaned a powerhead and replaced it (he thought) in the exact same spot. Apparently it wasn't quite exact. Haddoni's like low flow - if their oral disk is being moved by the current, it's too much and will cause it to move. Back to BTA’s, in the wild, even moving several feet over to the other side of a ridge is a small distance, bit may be across the tank in ours. Knowing the flow requirements will help you tailor the flow in the area of the tank where you would like the nem to stay.
Foot: This is my #2 reason why BTA's apparently move without known cause. The foot of most anemones also requires special concern. Some anemones like to bury in the sand, some at the sand/rock interface, and some directly onto rocks. BTA's like to have their foot in a deep crevice, hole, or cave. Basically, it's a safe zone for them to hide in if they need to retract. It's also a way for them to regulate the amount of sun it gets. These deep holes are key to keeping a BTA happy with it's current spot. They like their foot shaded, and head out in the sun.
Mechanical: Finally, mechanical reasons. Maybe a rock or coral fell or shifted and is physically touching the nem. Perhaps just because of growth by either/or the anemone or surrounding corals a once non-touching environment has turned to constant touching. At some point, the anemone may decide enough is enough, and move slightly to avoid constant nematocyst stinging. Also, there are animals (various fish/shrimps etc.) that pray on anemones. Constant picking by any of these animals will lead to the anemone retreating to a location where predetation is rediced or completely avoided. Unfortunatly, this usually coincides with less than optimal conditions of flow and light to help an injured nem recover. Think of your BTA like a balloon, don’t let it rub against any other corals near it, or let animals pick at it and you will be safe from mechanical damages leading to movement.
Hope that's a good summary of what I think about BTA's.
