I doubt the deer would do much damage, but cattle running into or rubbing on things can be a major problem. I am assuming that you are talking about the lift-up-on-top-handled water hydrants that drain back down to a valve at the bottom? These are not as stable in the ground as would be ideal, so protecting them sounds like a good idea. I think your plan of a triangle of 9' locust posts with roughcut planks sounds good.

However, and while not knowing your location, the height sounds like over-kill. You only need to keep the animals from touching the hydrant, not from landing on it, so I would think that half-length posts, giving you an approximate 3' to 3'6" barrier around the hydrants (18-24" buried in the ground) would be sufficient. This would also allow for easier access as you need to get to the hydrants to turn them on and off. Of course, if you are in deepest New England, where the frost goes down 4-6', then never mind, you NEED the 9' length, just to have a decent height above ground!!!

Thanks Dibbit,

Am just west of you and a bit north in z6/7-so will not plant the locust posts more than 24-20 inches in our tough clay and occasional brachiopod strata. Hydrant as you described and about 30" tall.

Have been thinking of a 4'-6' equilateral triangle design so there will be protection from loose animals. Might even incorporate one side in a blueberry patch fence (5-5.5' H.) I would trim the posts after I plant them.

Am planning to ask a roofer friend for scraps to lay on the ground, to reduce grass/weed growth.

So far no brilliant ideas for the second hydrant, but did come across a "saved" article on raising French Guineas in an elevated house...maybe, above the hydrant? with the same sized enclosure as near the blueberries.