What kind of vehicle are you mounting to? I have never had good luck trying to install a fender mount antenna with its coax cable. Never been able to fish it down through the firewall in either a Jeep or Ford Explorer without adding more holes than I wanted to. There are also the bent metal clip type fender mounts you screw to the fender under the hood; this ends up with a lot of cable just hanging out there that you have to bring in somehow. . .
Why mount the antenna on a fender when you can mount it higher up on the roof or window? It looks a little nerdy but I use a MFJ 310 MFJ Enterprises Inc. (or similar) BNC window mount with a radio shack 20-006 Center-Loaded Telescoping Whip Antenna - RadioShack.com center loaded adjustable whip antenna. You can separate the antenna from the mount and take it with you with the radio since the antenna telescopes down to about 6". With the loading coil engaged, this antenna is one of the few scanner antennas which tune down to VHF Low (30MHz). You can also put different antennas on the window mount, I have made an HF whip using 3 feet of piano wire attached to a BNC connector. You can also add uhf and vhf radial wires at the mount for better transmitting efficiency.