The most common type of plagiarism on term papers here at the University of Alberta tends to be the unacknowledged use of sentences or paragraphs from websites. Robert Harris lists several ways to detect plagiarized passages, including abrupt changes in style or diction, unusual or inconsistent formatting, and obvious references to facts or people outside the scope of the paper .
You may also find something in a term paper that sounds familiar. Keep copies of previous term papers, just in case you run across one that has been resubmitted or plagiarized by another student.
The University of Alberta does not subscribe to any of the plagiarism detection services but there are other ways to detect plagiarism from a website. Once you suspect misuse of a website, the easiest way to check it is to type a suspect phrase (in quotation marks to find the exact phrase) into a search engine like Google. Start with concise but distinctive phrases rather than an entire sentence or paragraph. Be alert to the possibility that some websites also include plagiarized material.
If you opt to use a text-matching software to detect plagiarism in student work, be aware that that use must be FOIPP compliant. There are also intellectual property and pedagogical implications that should be considered. If you use a software package that stores student work in a database, you must also provide an opportunity for students to opt out. See the Report on the Use of Text-Matching Software for Detecting Plagiarism in Student Work.
 Harris, Robert A. (2001). The Plagiarism Handbook. Los Angeles: Pyrczak Publishing.
Deterrence is always better than detection. Let students know specifically what you expect on labs and assignments concerning group work or collaboration on assignments. If you allow collaboration, how much is acceptable? At what point does it cross the line into plagiarism, cheating, or participation in an offence?
It's a good idea, if possible, to photocopy or digitally scan assignments before you hand them back. In the unlikely event that a student changes answers and resubmits the assignment for extra marks, you can compare the photocopy to the assignment to be sure nothing was altered (i.e. Misrepresentation of Facts).
Detecting inappropriate collaboration may be as simple as noting that two or more assignments contain similar or identical responses, especially in terms of diction, formatting or unusual formulations or mistakes.