I really really hope you don't find out the hard way about tying dogs up outside shops - it isn't just the attractive/expensive breeds that are stolen.
Dogs are also stolen for people to abuse - beat, kick, stab, drown..
Dogs are also stolen to ransom back to owners.
Dogs are stolen if someone thinks there is the possibility of breeding from them - and whilst you'd think being neutered would stop that, I've known of cases where the dog was taken, and then when checked and found to be neutered, dumped or, killed then the body dumped.
I just can't imagine putting one of my dogs at risk of any of that simply for conveniences sake!
I once left my scruffy terrier mix (neutered) with someone I knew 'ish' outside a shopping centre (he offered to mind the dog)... As I walked back through, some scruffy townie lad was running toward me with my dog! I grabbed the lead without even thinking and he ran off, but he had snatched the lead from the guy minding him and just taken off with him, very very luckily, in the direction I was coming from and he had no idea what I looked like.
A second or two later or if I had dithered or if he'd gone the other way, and I'd have almost certainly never seen my dog again. The guy who had been minding him was shocked and really upset but thought the lad had taken him to sell for drug money.
Please don't think it can't happen to you. It can, it happens to other people every single day.