poor dog! - & poor U, i know it's very worrying.
It's good that the vet will see him this evening, & also that U sent the photos - documenting anything that doesn't look right is a very, very good idea.
Since the sutures popped the 1st time, it might be that Ur dog is allergic to / reacts to the suture material - skin glue
might work better, or even surgical staples
[which must be removed, after the incision heals].
Dogs or humans whose skin reacts badly to a particular suture material may need to have stitches that use a different kind of "thread". // Possibly
even a butterfly clip
would be able to secure this incision, but only the vet who did the surgery knows the extent of the wound, inside & out.
All of these options are entirely up to the vet - no-one can tell, simply by looking at how long a cut is on the surface skin, what sort of closure it needs to heal properly, & even more importantly, there may be internal incisions that are deep, or possibly longer than the external cut. Incisions to remove something can have 3 dimensions, L x W x H, & there may even be a void where the tissue was removed.
We cannot tell what the inside of any incision looks like; only the surface is visible to our eyes.
Do U know if his skin broke or tore, where the stitches were? - that could be a sign that his skin doesn't get along with that suture material.
Or did he get his teeth on it, & pull the stitches out, or chew them, & / or his own skin?
Licking is definitely a bad thing, so keeping him from touching the area is important, to prevent infection.
U say he's "tied" to confine him - is he at home, tethered, while U are at work?
Or is he tethered nearby, where U can check on him?
I would worry if he was tied at home, alone - it needs to be very short, so that he cannot possibly get the tether tangled or caught on anything, plus it needs to be a material he cannot chew thru.
A crate is much safer - altho i understand that not everyone has a crate, i can heartily recommend buying a used airline-approved shipping crate
, so that if he needs to be confined again, U have a safe place to leave him, where he cannot get tangled, jump onto the sofa, get into the trash & eat garbage, & so on.
CraigsList & FREEcycle are both good places to look - generally, buying a used crate saves about 1/2 the new price, & they last for decades, thru many dogs.
I hope the vet can find something that will hold his skin securely, so the incision can heal properly.
Do let us know what the vet says, please, & how Ur dog is doing? I can understand entirely how worried U must be.