Hmmm, this got me thinking, Ladybird. So what if the fight started at home, Allison marches out in anger/fear/hurt, heads down Boscombe Rd, GBC follows on foot and catches up to her (Scraps barks as people near his place), GBC tries to muffle her yelling at him by putting his hand over her mouth, this prompts a shrill scream for dear life (heard by many) and a giant tussle in the grass (hence the foliage, which is probably similar around the area to the BC's carport) and he goes too far. Deliberately or otherwise, she stops breathing (it wouldn't take long). He lifts her over his shoulder, walks home praying no-one sees him (and no-one did), puts her in the boot, double-checks the kids are asleep and off he goes to Scout country. Woops, left the phone behind (perhaps it fell out of Allison's hand or pocket in the struggle).
This would explain:
(1) The fact the kids didn't hear anything.
(2) The fact other neighbours did.
(3) The behaviour of Scraps.
(4) The foliage in the hair.
(5) The location of the phone and GBC's semi-startled response to the police locating its signal nearby.
Of course, this doesn't explain why the phone wasn't subsequently found. Maybe he threw it in a drain near where the struggle occurred? Maybe he didn't lose it but instead brought it home, smashed it to bits and flushed it down the toilet, hence his surprise that it was still giving any signal at all.
Thoughts?