It is not possible to guarantee that metastability problems are avoided.
The MTBF for a circuit can be calculated, and you add synchronizer stages if you want to increase it.
From Altera handbook 12.1, Volume 1, chapter 14:
"Designers commonly use two registers in a synchronization chain to minimize the
occurrence of metastable events, and a standard of three registers provides better
metastability protection. However, synchronization chains with two or even three
registers may not be enough to produce a high enough MTBF when the design runs at
high clock and data frequencies."