I have no experience with this plant, but because I had not heard of it out in Michigan, I had to do some looking up... [Just always curious.] It apparently is endangered, at least in wild areas, in both Massachusetts and Connecticut. This might help with your father's problem!

Most groundcovers and such spreading plants spread by runners of one sort or another, below ground, and these things can often be very complex under the soil level. Pulling the plants up, even if it looks like you have pulled a lot of "root" with it, doesn't help much. New shoots sprout up from the underground parts.

But if it is endangered.... Do some searching re local/county/state volunteer or official organizations, garden clubs, environmental orgs, etc. You might find some who would send a few volunteers out to *dig out* your father's problem child, and move or ship it elsewhere, in MA or CT or elsewhere, where they would want to reestablish this endangered critter.

linda's right- posting it on freecycle or craigslist as a 'dig ur own' project may get you a ton of responses...

beyond that, a local wildflower conservation group will usually come out for a 'rescue' mission.

if all else fails- a flame weeder (leevalley.com carries two models- the bigger one uses a grill-sized propane tank) is your best bet- no 'pulling' needed, wilting the plant destroys the vascular system, and it dies. a session a month goes a long way to holding back the invasives!

This is from the original poster:
Unfortunately, the plant that is invading my father's yard is not the endangered one. The endangered one is the "wild strawberry" which has edible fruits. This one is just a nasty, fast-growing, spiny invader related to the strawberry plant (and the rose, too). But your suggestions have been helpful, although probably too labor-intensive and drastic for my 85-year-old dad to try. It will probably come down to pulling and digging again and again...

Baren strawberry, Waldsteinia frageroides is NOT spiny. I think you have Duchesne

Both of the plants known as False or Barren or Indian Strawberry, Waldsteinia or Duchesnea, have yellow blossoms and are not thorny.

I think your father's invader may be a Dewberry, which has white blossoms and is viciously spiny. I'm way out of my garden zone here, but all 3 of these plants grew in my old garden. The Dewberry was impossible to ever totally eradicate as birds spread the seed and the smallest bit of root would regenerate. Pulling up new sprouts with heavy gloves was my method, but I never had a heavy infestation...just an annoyance. Sorry I have no advice but if this id is correct, perhaps it will help you find your answer. josh

Here is a link that might be useful: Dewberry