Use white glue. When I ran out of setting solution someone told me to mix 1 to 5 white glue and water. It worked, but be sure you wipe off any extra glue around the decal. Also be sure to seal the decal as it isn't waterproof.
Berny
Phormer Phantom Phixer
On the bench
TF-102A Delta Dagger, 32nd FIS, 54-1370, 1/48 scale. Monogram Pro Modeler with C&H conversion.
Revell F-4E Phantom II 33rd TFW, 58th TFS, 69-260, 1/32 scale.
Tamiya F-4D Phantom II, 13th TFS, 66-8711, 1/32 scale. F-4 Phantom Group Build.