There is some learning required for using a tiller. Have your neighbor show you how to use it. Perhaps you didn't lower the drag stake and/or raise the transport wheels. Even after you do that, it takes several hours of using a tiller to learn not to "fight it" and to let it rock around and find its way, instead of trying to "over-control" it. Don't get a "death grip" on the tiller and don't strain your back or arms. Front-tine and mid-tined tillers get a reputation for being hard on the user because you do need to learn the proper technique to use them effectively. The problem with borrowing a tiller to till rocks is that you run the risk of breaking the tiller or yourself.

Our soil here also has a lot of rocks, so I use a mid-tined top-of-the-line Merry Tiller. Its slow tine speed and controllable high tine torque let me "roll out" some surprisingly large rocks. I till once or twice a year, so I have accumulated a large rock pile from rocks that my tiller has "rooted out".

My Merry Tiller's triple reduction transmission and dual V-belt transmission give it unique ability in heavy rocky soil and, by allowing it to proceed somewhat slowly, I can till much deeper than its rated 12 inches. I routinely till as deep as 16 inches, which is about equivalent to double digging with a spading fork or spade.

The top-of-the-line International Merry Tiller is expensive. If an investment in it is beyond your budget, you might want to purchase a good spading fork and spade. Double-digging a garden plot is good exercise, and before I got my Merry Tiller, that is what I did.

If you hire your soil tilled, the guy will most likely use a rear-tined tiller which has a high tine speed. A high tine speed doesn't work well in rocky soil and, even without rocks, a rear-tined tiller has a hard time tilling 6 inches deep. Most hired tilling jobs aren't that deep, and usually amount to a pulverized veneer about 3 or 4 inches deep. The hired job looks well-tilled, but that "beauty" is only "skin deep".

Rocks are tough on most tillers, so if you hire your garden tilled, get someone with a farm tractor and a stout one-bottom moldboard plow.

MM

I think you are expecting too much from that machine.
IF your clay is hard packed, hire out the initial tilling. Otherwise, you'll just beat yourself and the machine to death!
Often you can find people that do smaller plots in the garden section want ads or Craigslist.

you could remove the rear wheels and stick the spike in the ground and let the tines dig the depth you want then lift up on the handle and move a few inches. Very slow work and take small bits out of the hardpack. Packed dry clay is like trying to till rock. So it may be wise to let a tractor with a PTO tiller bust it up. But, I've done it before depends on what you have to work with and there is always the shovel if you don't want to hire it out. my grandpa use to shovel over a large garden, he done that for about 60 years.