I had the same problem with both my dogs. Shaianne used to get in it and I would just yell at her and she would leave it alone.
Keegan as a puppy monster was another story! She got in it one night and got stuck!!!
So My dad built me a huge walk in closet and I requested a kitty hole for Kylie and problem solved. At first Keegan would try to put her head in it but it works great.