i wouldnt worry too much, itll grow back up very quick. if its too brown underneath to really make any good growth, replacing it all might be the way.. i woudlnt expect it to last forever tied down as its not its natural position.

I trim mine up weekly, so it looks more uniform.. as you can see, some of mine is probably 1.5 inches deep in places now, when it starts dislodging itself, ill just replace it with some more and start over.