Dog keeps hopping the fence.

We recently moved into a house that has a back yard and my dog keeps getting out by hopping the fence yesterday she got out and then ran off took an hour to find her. The two other times she came straight to our front door. I don’t want to have to keep worrying about her getting out and lost. She loves to be outside. We lived in an apartment prior when we got her so this is the first time she has had a yard. We don’t have anything up against the fence that she can use as a launch pad. She a Belgian mal so jumping fences is what they do. I haven’t had this issue with my other mal I have. What can I do to keep her in the yard???? I want to be able to put her outside so she can run around as much as likes. I can’t sit and watch her the whole time because I have a very active toddler. Please help.