I'm going to build something for commercial use to "dethatch" and tear the ground a bit for better seed to soil contact for grass seeding. This would be patches of existing grass under trees where I'm not comfortable with more aggressive equipment that might damage tree roots. I need stronger and more durable tines than baler tines and will use tedder tines or maybe even the 3/8" tines used on some harrows and such. The implement will be roughly 8' wide to cover my tracks so one tine every inch in the plan. It will work and I've made and seen similar ideas in the past.
What about using a Land Pride Spike Tooth Harrow? Spike Tooth Harrow will give you considerable 'reach' under trees.
LP STH15has one spike for every 1-3/4" of coverage. Note: 10 settings for tine angles.
STH15 Series Spike Tooth Harrows | Land Pride
Of a common Landscape Rake? Landscape Rake will have more ground contact, however you could remove every-other rake tooth.
Or consider a suspended Chain Harrow. The one I assembled has 1/2" chain. For commercial use I would use 3/8" or 1/2" chain. Suspended, you could scuff under trees.
http://www.tractorbynet.com/forums/...c-countyline-tarter-boom-pole.html?highlight=