Stanley has been another dog that has been resisting heat.  I don't blame him one bit!  We have been having some behavioral problems with him not walking in general.  After training sessions, great ideas (and great food bribes), we are seeing improvement!   What I have learned with him is that he gets anxious when his mind is not focused on something.  His brain needs to be challenged.  When he gets his leash on, he gets a treat.  We go outside and he puts the breaks on.  I get him to focus on a small treat.  I then throw it as far as I can and make it a game of "let's find it!".  he seems to respond to that! If I find it first I pick it back up.  If he finds it first he eats it. We do this maybe 2-3 times until he is walking well.  Then in between I have him sit and high five/give me paw every half block or so.  He gets a treat then too.  He seems to enjoy having a task and has been much better outside.  No barking.  No laying down.  I'm the treat gal! :)
I love my big Stan!