Spider repellent not working!

2 weeks ago i plugged in a sonic spider repellent, and have been congratulating myself that I hadn't seen a spider in 2 weeks ...... until tonight!

But why do the buggers always have to be right at the top of the blooming wall? AND behind the Rabbit double cage! We (the royal we) had to pull out the double cage (thankfully on wheels) to get to the spider - and OMG! the mess behind was shocking! How comes there is SO MUCH bunny fur there - the rabbit should be bald!!