has your 8 yr old played rough with him/tug of war?usually if 1 member of the family is the dog toy the dog will always go back and sees the person as thier toy,ask your son to totaly ignore the dog at all times until the dog realises that your son will not play with him,also up the excersize especially before your son gets in if you can,try some training ie sit,stay,fetch,high five lol,all the basic training will get rid of all the pent up energy better than a walk ,mental excersize really does make a dog tired ,and try and be firm ,bulldogs love nothing more than to bully a human into submission ,they want constant attention and can be a real pain,also use a squirty bottle on him ,the dog not your son lol,i still have my bottle to hand and when i bring it out then annie immediatly stops what shes doing,but ignoring bulldogs is the best way they hate it,it may take a while to work but it will work,karen