Rust on shade cloth post

When I bought the house I paid a painter to grind the rust and repaint it. That was 2 years ago but it's back. 3 of the 4 posts have it. My Dad reckons they didn't grind it properly, I suspect the rust is so embedded there is nothing I can do.

Any advice? I won't be able to redo the poles myself (and I imagine it will cost big $$$) but any advice even to stall it for a few years would be helpful.

When I bought the house I paid a painter to grind the rust and repaint it. That was 2 years ago but it's back. 3 of the 4 posts have it. My Dad reckons they didn't grind it properly, I suspect the rust is so embedded there is nothing I can do.

Any advice? I won't be able to redo the poles myself (and I imagine it will cost big $$$) but any advice even to stall it for a few years would be helpful.