From the OP's description of their problem it would appear that their chassis is unable to cross the bump and I will assume this when suggesting strategies.
First of all there is "block'em all" strategy. For this strategy to work (properly) the opposing alliance must consist of a good team that traverses the bump. If you orient your robot parallel to the bump and block the opposing robots ability to cross you will force them to use the bridge. While this does necessarily reduce the points, it will slow down the opposition, and you know what they say....time is baskets
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That said, a simple modification to the standard C-Base chassis will allow bump traversal and that in and of itself will open up massive defensive and future offensive possibilities. On a side note: a wide bot will be better for the bridge, however it will be worse when it comes to stability while playing defense. Try to keep in mind how likely a 3-robot bridge balance will be. Also, on robot modifications...a simple sprocket reduction for extra torque will go a long way in terms of defensive capabilities.
Often Team 1325 has played defense (usually with end-game capabilities) and to train defensive drivers takes a lot of co-ordination. First of all, the three members of drive team must know every single rule like the back of their hand!! Especially this year!! The way we set up our defensive drive team is:
Coach: Surveys entire field and determines what team to block and where
Driver: Executes the Coaches instructions
Secondary Driver: Is the Timekeeper/End-game specialist
To practice, have the drive team set back from the robot (Driving on Carpet) to get used to being distanced away from the robot. Also have your drivers practice with safety glasses on so they are ready for competitions.