Leavening your dogs unattended is a seriously "high risk venture!" Pretty much no way around that, that said ... the ability to do that is gonna depend on the dog and the environmental factors??? How close is traffic and what will your dog do if someone approaches and attempts to pet???
Most likely you can answer the first question but the second question ... not so much??? My particular (formerly H/A OS GSD) is apparently extremely handler dependent! If he is in an out sight "Place" and someone attempts to approach him ... he makes an independent decision and he will "Break Place" and "Walk Away!" That is just fine by me! I've had two "crap happens situations?? And one involved a toddler ... and under extremely controlled circumstances ... he provided not to be a fan of toddlers! I don't have kids, so I don't intentionally expose him to kids ... still crap happens???
And one day when at a clients with Rocky (I'm a PCA), I had Rocky out back in Place and unexpectedly Grandma showed up with a toddler! Well that was unexpected but Grandma has the kid ... well, Grandma fell asleep! I finished up with my client and I was first to notice the toddler was gone!!! I freaked and rushed to the back dog!!! I opened the door, expecting a scene of horror and found the toddler unharmed but ... no Rocky??? So first there was relive and then confusion ... where was Rocky??? I scanned around and found him 15 feet away! Most likely he saw the toddler approach and his default is "apparently" we don't bite people but where is dad??? No dad to be found so he made an independent decision to a non threat and ... walked away! On another occasion at our local quick market ... where he routinely goes in "Place" no leash it's just a command and it means "Stay here and don't move." As I was coming out of the store ... I saw someone approach him!! As I was preparing to scream at them ... I observed Rocky ... once again "Break Place" and step away from a stranger, yet again ... no Dad to be found??? And "Rocky I don't know you ... I'm outta here" he broke Place and stepped away!
I did not train that particular behavior per se, but I did train him not to be "biting the crap out of people and stuff" when he is with me! But you know if Daddy is no where to be found??? Then it comes down to ... make good choices dog! Third occasion, a stranger told me where he was?? I came out of the store and Rocky was not where I left him?? A different stranger said he's to the right of the doors?? Apparently while I was out of site ... yet again someone approached him and yet again ... he walked away! Most likely not ideal "Place means Place" but I'm pretty grateful for his "apparently"default behavior to walk away ... when there is no "Daddy to found??" He gets no grief from me!
And my Boxer Struddell yeah ... nope never 8 years and no out of site "Stays and or Place!" I actually had to theft proof her! She was a dog that would happy drive or walk of with uh anyone ... it's a Boxer thing.
But back on point ... I get why you want to leash your dogs to an object to secure them?? But the fact that they are leashed ... is most likely the source of the problem??? A variation of "leash Barrier" reactivity?? Because the dogs can't move from this spot .... it causes stress??? If you can't trust them to "Place" then most likely you can't trust them when they are out of site???
I understand you are talking about minuets, if ... you train "Place" you can "Proof that under controlled conditions with distractions! Outside the confines of a Dog Park is ideal! And I suppose you could elicit the help of Dog Park strangers ... to see what your dogs would do if approached??? I'm gonna assume you don't have H/A dogs to even consider that of course!
But ... if you secure to an object ... then you best sure your dogs cannot move that object! there is a Boxer tragedy behind that advise! IF you don't or can't currently trust your dogs to stay in place while leashed??? I suppose you could train that at home?? Lash them to whatever at home and get them used to being restrained by there leashes?? It's not something I've done but it makes sense of course if they are restrained ... it removes there ability to walk away. So that is more of a flight or fight situation, if the dog is restrained??? It's not a choice I would make.
At any rate "Place and Sit on the Dog" details can be found here. :
Fearful, Anxious or Flat Crazy "The Place CommanD - Boxer Forum : Boxer Breed Dog Forums
But understand ... that if you have your "eyes off your dog" in a public situation ... you are taking a risk!! Some dogs can handle the unexpected and some dogs cannot. If your dogs are out of site in public ... it is a high risk venture.