If anything "don't know" could be in the middle:

1. Agree Strongly
2. Agree
3. Don't Know
4. Disagree
5. Disagree Strongly

Here's a similar Likert scale discussion.

If anything "don't know" could be in the middle:

1. Agree Strongly
2. Agree
3. Don't Know
4. Disagree
5. Disagree Strongly

Here's a similar Likert scale discussion.

Also, as @PeterFlom noted, you have more "agree" answers than disagree. Likert himself recommended using equal number of right and left answers. The paper is rather fascinating, btw, I suggest reading it in full.

If anything "don't know" could be in the middle:

1. Agree Strongly
2. Agree
3. Don't Know
4. Disagree
5. Disagree Strongly

If anything "don't know" could be in the middle:

1. Agree Strongly
2. Agree
3. Don't Know
4. Disagree
5. Disagree Strongly

Here's a similar Likert scale discussion.