Dan, I apologize for the delayed response. Here's some information on Canada thistle.

Canada thistle (Circium arvense) is a creeping perennial, reproducing largely by rhizomes (i.e. underground stems). Canada thistle can also produce seed, though this is not the main means of reproduction and spread. Canada thistle has lobed leaves with smooth upper surfaces and sharp-tipped spines on the margins. The roots of Canada thistle have been measured down to 6 ft, with the majority found between 8-16 inches. Most other thistles such as bull thistle are biennials, meaning they spend one year as a rosette and then send up a shoot with flowers in the second year. Bull thistle (Cirsium vulgare), has rough hairs on the upper leaf surface and has a taproot, usually unbranched, and no rhizomes like Canada thistle.

Removing the aboveground growth can eventually starve the root/rhizome system, but this often takes several years (multiple efforts per year) depending on the level of establishment.

Impermeable mulch (plastic mulch) may help, but if there are any holes in the mulch for desirable vegetation, it is likely Canada thistle will exploit those. Organic mulches (e.g. wood chips, bark, etc. ) are not effective, as you are finding.

Herbicides are often the fastest option to gain control over a Canada thistle population, but given the location of this infestation, plastic mulch covered by woodchips and/or frequent mowing/weed whacking are probably the best options. 

If there is a period of low activity when an herbicide application could be made and you'd like more information on that, please let me know. 

Thanks for the reply.
You have given me information that I didn't find so that's good..
But based on the information I did find we bought a garden fork and have been attacking it with that.
I do appreciate the time you took to give me that reply though.
All good info
Dan