Hawkeye...
The same as a shoe repair guy would use,well used on my own shoe making bench
Rough up both sides and coat them with ordinary contact cement in a well ventilated area. Let 'em dry all the way.
Then give them both another shot and use low heat on the heat gun on both surfaces.
Once you mate them it'll be real hard to get them apart.
Trim the excess.
They will be okay even when wet, but will separate once the leather is soaked through and through.
Don't shoot yore eye out, kid
Capgun