I’m thinking about getting one of these motion sensing sprinklers to keep the deer away from my roses next spring – and from decimating the Nasturtiums as well. Seems to work fairly well for deer, some say. 
But not for all animals, says this review from Amazon.com:
does not work, June 29, 2009We installed it about a month ago. Now the geese walk real slow so that the motion beams are not tripped and they walk right up to the back patio to eat my grass and leave me little “presents” all in my yard. This morning, one goose was actually drinking the water sprayed from the Havahart 5265 Spray Away Motion Activated Water Repellent. They have gotten used to the spray and some even wait out the 8 second delay or get behind the chairs on my porch to wait out the 2 second spray then continue to eat and **** in my yard. They even circumvent the whole system. (We installed 2) We have even moved the system around to fool them which has not worked either. Thanks but no thanks. I would not recommend this as now I have more than 40 geese take up residence since it was installed.
Well, that’s OK – I plan to get the other brand anyway! 
Like water off a duck’s back.