Here's a little interactive session on perimeter with Amy and Ben who are building a new pen for their dog. Your student has a chance to check their answers, move a virtual ruler around more polygons, etc. For more online practice, perimeter lessons start in the geometry portion at the second grade level at ixl.com.
One teacher had his students measure the perimeter of candy bars! If in your mind that encourages bad habits (or makes the teacher in your home crave chocolate), you might try cereal boxes and others in your pantry.