I'm sure someone with more experience will be able to tell you more but I will tell you what I have found works for me.
First according to the instructions that came with the walking feet for both my machines, you shouldn't backstitch with the walking foot. When I start quilting I take 1 stitch and use the top thread to pull the bobbin thread through to the top of the fabric, then continue stitching. When I reach the end of the line of stitches im sewing I take an extra stitch then cut the bobbin and the top thread. I use the top thread to pull that last bobbin stitch up enough to use a pin to pull the bobbin thread thtough to the top. When I get a bunch of hanging threads I take the time to knot the two threads then use a needle to hide the threads into the quilting between the top and the batting. I have been told by others that this will secure the threads and it shouldn't come apart anytime soon.
I don't know if this makes sence but it is working for me but I will be interested to see if someone else has more ideas. Good luck.