Osage Orange (HedgeApple) is a VERY GOOD wood to use as cover....it will last a lifetime or more....BUT YOU STILL HAVE TO ANCHOR IT!

Here's a small bit of info....for more, go to Maclura pomifera - Wikipedia, the free encyclopedia

"The heavy, close-grained yellow-orange wood is very dense and is prized for tool handles, treenails, fence posts, and other applications requiring a strong dimensionally stable wood that withstands rot.[23] Although its wood is commonly knotty and twisted, straight-grained Osage orange timber makes very good bows. In Arkansas, in the early 19th century, a good Osage bow was worth a horse and a blanket.[8]
When dried, the wood has the highest BTU content of any commonly available North American wood, and burns long and hot.[25][26][27] The wood should not be used in open fireplaces without a spark screen because the wood is very prone to popping and may send sparks and small embers several feet."

"Unlike many woods, Osage orange wood is very durable in contact with the ground. Smaller logs make good fence posts, being both strong and durable. They are generally set up green because the dried wood is too hard to reliably accept the staples used to attach the fencing to the posts. Palmer and Fowler's Fieldbook of Natural History 2nd edition, rates Osage orange wood as being 2.5 times as hard as white oak (Quercus alba) and having twice the tensile strength."


But, Osage is not the heaviest or densest wood....look up IRONWOOD and it will give a list of the various trees and shrubs that fall under this category.
You still should be safe and anchor anything you put into a Public body of water...if this is for your personal Pond, then drop away!