I would not give up without thinking about it a little more. I know
you have the design already done and approved, but do the spikes have
to be square?

I am thinking 1/2 inch copper pipe with 1/2 inch steel rod inside for
the spikes. And a pointy copper arrow head added to the top
afterwards. If it really has to be square, then make a tapered steel
piece and pull it through either 1/2 or 3/4 copper pipe. Obviously
this will take some experimentation. But I think it could be done.
Start with copper pipe that is longer than you need and braze on at one
end something to hold it. Use 1/4 inch steel cable and a come-a-long
to do the pulling. You may have to make several square tapered steel
pieces of increasing size and anneal the copper pipe after each pass.
And of course use lube. I can see you now doing this between two
trees.

If you can make square copper tubing, then you can use two of them
brazed together ( or welded ) to make your 1/2 by 1 rectangular bit.
Or if you can use rounded pieces then two copper pipes side by side or
spaced so the " spikes can fit between.

Whitman college in Walla Walla, WA has some gates made of copper pipe
that are attractive. As I remember they are of quite a bit bigger pipe
and so probably don't have the steel inside.


Dan