What's the best way to get telemarketers off my back?

It depends on which country you live in. Here in the UK you can register with the TPS, Telephone Preference Service, to try to ensure that you don't get unwanted marketing calls (unwanted = none in my books). Sometimes the odd caller will slip through but when they do get through to me, I am very sharp with them and ask them initially "What is your company name?" and then make a note of it before telling them quite clearly that I registered with TPS to avoid getting nuisance calls like this and that I will report them so they had better remove my number from their records quick time! My number is ex directory so I rarely get calls but some shoddy companies use random number generators which is very annoying but I am sure they are supposed to check with the TPS as to who is on their list so as not to harrass them.

im not sure about canada but here in the USA we have a do not call list to be put on. it really helps.