I can sympathize with you,Saffy, because Spike can be an absolute devil at recall if he's busy hunting out his rabbits!! Even as a a young puppy when they are supposed to stay close to your side Spike was off & away totally deaf to all my calling; I could bellow until I was blue in the face with no result!!
I also tried taking a toy with me - Spike ignored it - hiding - he didn't even bother to look for me!! - having
fantastic treats for him when he did come - he took the treats when he felt like coming back - training classes - his recall was perfect in the class & the amount we did he should have been ready for Crufts! - & finally castration in desperation which took the edge off him but still didn't result in the instant recall I craved!!!
Having read CraftySam's thread on whistle training I started giving that a try & I must say Spike's recall has improved in leaps & bounds. I think he had got used to ignoring the word 'Come' so now I blow the whistle & as soon as he comes to me (& he does now!!!) he gets a squirt of Primula cheese. I try not to keep calling him & try to only use the whistle when I'm fairly sure he'll respond but so far (touch wood!!) he responds really well. I followed Sam's instructions & got Spike used to the whistle indoors with no distractions first before progressing to the great outdoors.
However if I'm somewhere where I think the dogs will be distracted & there's a dangerous road for instance I'm afraid they go on their long leads; better to be safe than sorry!!
I do think though that some dogs are better at recall than others; my lab, Sid, never left my side from day one; in retrospect though I think the labs weren't so much good at recall as much as they didn't actually run off & I could always intercept them if needs be - Spike has always tended to go off & never felt the need to stay by my side like the other dogs did!!
I would definately persist with the whistle with Saffie; it certainly helped Spike!!