Quentin:
You didn't mention whether or not you are using staples, but if you are, try using wire brad nails in those areas that are prone to pull away. You can drive the nails through small scraps of strip (2-3" long) to help exert additional pressure. Another option is to get a cam-ratchet strap around the area and exert some pressure all the way around. The picture below shows a strap in action dealing with the exact problem you describe. You can see a piece of strip under the strap to deal with a specific area.

Regards,

Marcel