If you have reason to believe that a spell has been cast on him, then your first order of business would be removing it, rather than casting another spell.
If he practices magic himself, a cleansing bath or other similar measure should suffice for most purposes. A more stubborn spell might require several baths, possibly with the incorporation of other tools like a stone designed to absorb negative energy. Black Tourmaline would be ideal.
If he doesn't practice magic and isn't open to the idea, then things get trickier. You can try and unravel the spell externally on your own if your ability to perceive energy is good enough to see the spell, and you're confident in your own ability to pull it off and ground it out. Failing that, a discreet cleansing ritual might be possible.
Once you've got the current problem solved, it's trivially easy to put a shielding charm on a piece of jewelry or some other token or keepsake. There's an example spell along those lines on the front page at the time of this posting. If he practices, the best bet would be to make him a talisman and have him work on his grasp of the basics, particularly grounding and shielding.
If he doesn't, your safest bet would be to give him a shielding talisman of some sort as a birthday/holiday/anniversary gift. Just make it something small that he can carry with him and without needing to think about it. A ring, a token to keep in his wallet, or some such.