Nobody can prevent a soft fork from taking place due to its backward-compatible nature but also the minority chain (assuming the soft fork was minority like if OP did it on his own) can easily be attacked by breaking the rule they enforce and forcing them to reject the block containing such transaction effectively forcing them to split.

For example take OP_CheckLocktimeVerify case. If it were on minority chain, someone on majority chain could mine a block that had a big number like <220f9212c18d0d0c> OP_CLV OP_DROP and for majority chain the OP_CLV would be a OP_NOP so they don't do anything while the minority chain sees the big number and rejects it as invalid (can only be 5 bytes) hence splitting.