Does anyone know anything about gardening?

I'm end of terrace and have a 6' wall at the edge of the garden leading on to the street. I'd like to make this a bit more burglar proof (but not looking shit). Current thoughts are:

1. Some form of low spikes. Don't want anything that looks shit or makes it look like a prison so not sure what the options would be there.
   
2. A trellis. I've seen suggestions that you can get weak ones that collapse under a person's weight and make it awkward to climb. This doesn't seem to be an advertised feature though so not sure how you pick out ones that are a bit weak. Also concerned about it blocking the sun as that's the direction it comes from in the evening.
   
3. A low planter attached to the top with some low lying spiky plants. Can't find anything quite what I want online so would have to build something. Not quite sure what plants would go in there though.
   
   

Spiky bushes on the inside have been ruled out for a number of reasons (we like the look of the wall, small child and part of the wall is a narrower passage).

Anything else I've missed? Any suggestions for what spikes or trellis to go for or what low lying spiky plants there are? Cheers