Keeping kikuyu at bay

I hope anyone have experience with this.  We have a Kikuyu Grass (Pennisetum clandestinum) lawn.  It makes a lovely lawn, but it is quite difficult to keep at bay!!  It loves anything compost rich and wet and for that reason would take over the garden beds.  I don't have any beds near the kikuju for that reason.
Is there any way that anyone know of that would work to curb it's conquest of my garden? 
I just wish to keep it where is currently is - but come the rainy season in a month or so it'll want to grow and conquer!!
Thought of planting fennel at the edge of the lawn.  I understood nothing likes to grow around it.  Would it work or am I naive and misinformed? 
I would try anything to keep my lawn from invading my food forrest.

Pls if anyone can help.


Suzie

I would start by getting a roll of metal roof flashing from the hardware store the type thats about 12 inches wide and burying about 10 inches of it around the garden beds for a border that should stop enough of the grass roots that what makes it across can be pulled by hand