When the men of the place asked about his wife, he said, “She is my sister,” for he was afraid to say, “my wife,” thinking, “the men of the place might kill me on account of Rebekah, since she is beautiful.”
Genesis 26:7 (NASB)
In Genesis 26, we all notice that Isaac is doing what his father did: lying about his relationship with his wife due to fear.
Abraham does it twice; both times, Sarah is taken.
Here, Isaac does it, but nobody comes and kidnaps Rebekah.
There are two proposals given for why:
1. Rebekah was not beautiful. Jacob thought so, but nobody else did; nobody wanted to kidnap her.
2. The people of Gerar remember the story of Abraham, and how God punished Abimelech for taking Sarah, so they no longer kindnap women.