The rehab idea is a good one---but to be clear: you don't catch him! The rehabber/s might. They have ways, using netting, sometimes a decoy. But without experience and proper equipment, it can be extremely dangerous to handle a raptor (your hand or your eye could end up looking a sight worse than that bird's chest!). And in any case, a far more likely outcome than you catching the bird would be the bird simply freaking out and flying away. Definitely call the rehab place if you're willing to, but after that your work is done.
My guess is barbed wire fence or somesuch... but who knows?.... Poor guy/gal!