Brettski :

Tires can be used in a number of different ways. Look at this slide show link from ahvatsa's pond where he partly burried some large tires and put some out flat. Others will put them tied together in mounds or fences. It really depends on your pond plan. Don't count on anything using them as a spawning area. I prefer using other natural objects like trees, rocks, brush ,gravel, pallets , stumps and dirt mounds and ditches for structure and cover.

http://photobucket.com/albums/b165/ahvatsa/

Here is a link to the structure manual :

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=000123

http://www.sdafs.org/reservoir/manuals/habitat/Main.htm

Last link below is for tires :

http://www.sdafs.org/reservoir/manuals/habitat/tires.htm