Thank you very much for all your kind answers.
Our basenji is almost 14 years old and we have her since 1996. She had never been alone before because our two dogs passed all the time together, they were inseparable!
Luckily my partner works at home, so we do not have to leave her alone for a long time. But even if she stays alone for less than an hour, it is too much for her.
Our backyard is not fenced, and our basenji does not like to stay outside for a long time. She loves warm places and often sleeps under the blanket. As to an inside pen, I think it would be a piece of cake for our dog, she would be perfectly able to destroy it in a few minutes…
We have tried to leave radio on when we are away, but as she is almost 14, she does not hear very much any more. We have not tried TV yet, it could be worth trying.
We have been thinking about another dog, but for the time being it is not an option. In fact, we would like to have a "dogless period" after this dog. We both leave far from our home countries and would like to be more free to travel back home.
Please don't give up, we need some more ideas...