The phrase "fencing in" can have a variety of synonyms, depending on the context in which it is used. Some alternatives might include "restricting," "confining," "enclosing," "hemming in," "trapping," or "boxed in." Depending on the degree and type of constraint implied, other options could include "constraining," "limiting," "curtailing," "hampering," or "stifling." In cases where the phrase is used to describe a more positive type of enclosure, synonyms might include "protecting," "shielding," "defending," or "safeguarding." The appropriate synonym will depend on the intended meaning and tone of the sentence in which it appears.