https://blogs.oracle.com/solaris/understanding-oracle-solaris-constraint-packages
install the solaris-11.3 constraint pacakge, that will ensure that you stay on the 11.3 release train and not move to the 11.4 train without explict action.
# pkg install pkg:/release/constraint/solaris-11.3
For more information see https://blogs.oracle.com/solaris/understanding-oracle-solaris-constraint-packages