I've got an old leather collar and if they play up I'll let out a few roars and give them a quick lash with it over the ass if I think they really have taken the piss. It's not going to cause any damage at all, it's a quick sharp pain to correct bad behaviour, and in all honesty I can't remember the last time I've had to give them a lash?
I also reward good behaviour and besides their daily walks I spend time with them each day in the garden, give them a fuss and all that crack. I find when you take a little time out for them you get a good bond with the dog that way, and you build up thei