please help...we need to find where to buy a fenced in pen...

hi, we are currently needing a fenced in pen for our pit Duke...he will be on heartworm vaccs for a while and the vet told us he cannot roam or run around for a few weeks. Hate having to restrict him but we want him to be healthy... Does ANYONE know where i can get a fenced in pin for him? DOn't really know what size but it's only temporary and we really need this... thank you :)