I have been using Digital Guardian for approximately 13 years.

I've used the solution for less than a year.

I have been using Digital Guardian for more than one year.

I have been using the solution for two years.

I've dealt with the solution for three to four years. 

I’ve used the solution for more than one year.

It's been around four years that I've worked on this solution.

We've been using the solution for about three months.

It's close to three years that we have been dealing with Digital Guardian.