Dig a smaller pond (sediment pond) that is easily cleaned out 1x year. That will trap the sand before it reaches the main pond. Plan on cleaning out that smaller pond once a year, or you will be draining/renovating the big pond sooner than you'd like.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
http://www.pondboss.com/subscribe.asp?c=4
3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).