Gave up weedwacking years ago. What a PITA. Running out of li ne, hard starting, etc. Life is too short. Get some Total Vegitation Killer (like Roundup) and spray where you don't want grass. Along flower beds (spray carefully and not in a strong wind), driveway, etc. You'll get about a 2" wide dead area along those areas, but sheesh...who cares? Haven't started a weedwacker in 3 years.
It would cost him more in chemicals than labor. And he needs the vegetation to come back. For erosion, of did you catch that?