Ideas needed...

Mel.. We had to tackle clay up at the farm veg plot. I know you are only talking about a border, but just scale it down for your border. Clay soil is known as a heavy soil - i.e. it lies heavy on the spade. Such soil cracks badly in hot dry summers and is sticky and unworkable in winter.
A clay soil is really river mud or river silt - tiny particles torn from the older rocks.
Although us gardeners dislike a clay soil - a good clay soil is one of the best soils a garden can have as almost any plant will grow well in it. In fact clay makes a good soil if properly drained.
Clay soils are chemically and nutrient rich, being formed of varied particles. But it has the serious disadvantage that its fine, close material retains the water and will not let it run away quickly enough.
Plants grown in a clay soil can become waterlogged, and eventually die of drowning. Therefore a stiff clay soil should be mixed with organic compost, leaf mould and sand or ash, to improve drainage.We dug so much in it was amazing, I have a wood burner so always saved the ashes, saved all my leaf mould & dug that in & had a couple of load of mushroom compost & it has paid off..

Stones will help drainage in a clay soil. Never remove the stones from a clay bed. If you do not like the look of them, dig them underground.

After digging in the Autumn the surface should be left rough to allow the frost to break up the lumps.
An application of lime will help to sweeten the soil and straw manure, sand, organic compost etc, will help to lighten a heavy clay soil if dug in in the autumn... :dh: I hope that has helped explain anyway..

 

Carefully! [Sorry that wasn't helpful was it...]

Spread on top and gently fork in; you shouldn't damage too many roots that way and the worms will drag it down over time. More organic stuff on top of the forked over and now worked in soil and you'll be well away