"dog" will not come up for a search for "dog collars"
right now, even if you enter the term in the box labeled "exact" - you get dog collar and everything else.
Of course, if your keyword is "music" or something - you might have to get a second mortgage on your home to do this, but if it is "proctologist", you are probably pretty safe.
The Google FAQ says to surround required exact matches by square brackets, example:
[rope]
The ad won't be shown if the user looks for "money for old rope" or "old rope prices", only a search for "rope" will trigger it.
This seems to get estimates without an account, so it may be what you want.
The FAQ is at:
[adwords.google.com...]