[CentOS] What on Centos is wiping out my eth0 IP address every 5 minutes?

QUESTION:
Why does my Centos 6.4 laptop keep wiping out my eth0 IP address?

SUMMARY:
a) I set the IP address of eth0
b) Everything works fine for 2 to 5 minutes
c) Then, that eth0 IP address is (somehow?) wiped out
I frustratingly repeat that abc process (over and over and over again)

BACKGROUND:
My home network has been working perfectly and there is no problem 
with my home network, nor my wlan0 WiFi access from my Centos 
laptop to that home broadband network.

Inside the house, I never use the wired (eth0) NIC; but, I'm trying
to set up a wired/wireless connection outside the house and that is 
where I'm running into this problem where Centos (automatically?)
constantly and repeatedly wipes out the IP address I set on eth0. 

I can easily (constantly) change the IP address of the eth0 NIC back
to what I want it to be; but that IP address only stays set for 
about 2 to 5 minutes; and then it wipes itself out (again & again).

Why? How do I stop this?
(All I want is for eth0 to *stay* at the IP address I set it to!)

To give you more contextual detail, here's a typical sequence.

SIMPLE BASELINE:
 Wireless NIC (wlan0) is turned off using a hardware switch on the 
 outside of the laptop (so that only one NIC is in play).

STARTING POINT: (eth0 has no IP address)
$ ifconfig eth0
=> eth0 Link encap:Ethernet  HWaddr A0:BE:C1:D8:E5:F1  
=>   inet6 addr: fe80::f2de:f1ff:fe38:8591/64 Scope:Link 
=>   UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
=>   RX packets:3139 errors:0 dropped:0 overruns:0 frame:0
=>   TX packets:3230 errors:0 dropped:0 overruns:0 carrier:0
=>   collisions:0 txqueuelen:1000 
=>   RX bytes:2403080 (2.2 MiB)  TX bytes:547895 (535.0 KiB)
=>   Interrupt:20 Memory:f2600000-f2620000 

I EASILY CAN SET THE IP ADDRESS of eth0:
$ sudo ifconfig eth0 192.168.1.100
$ ifconfig eth0
=> eth0   Link encap:Ethernet  HWaddr A0:BE:C1:D8:E5:F1  
=>        inet addr:192.168.1.100  Bcast:192.168.1.255  Mask:255.255.255.0
=>        inet6 addr: fe80::f2de:f1ff:fe38:8591/64 Scope:Link
=>        UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
=>        etc.

At this point, I can now connect a wire from the RJ45 port of the laptop, 
to the device (which happens to be a radio set to 192.168.1.20):

$ ping 192.168.1.20
=> PING 192.168.1.20 (192.168.1.20) 56(84) bytes of data.
=> 64 bytes from 192.168.1.20: icmp_seq=1 ttl=64 time=1.38 ms
=> 64 bytes from 192.168.1.20: icmp_seq=2 ttl=64 time=0.339 ms
=> 64 bytes from 192.168.1.20: icmp_seq=3 ttl=64 time=0.255 ms
^C
=> --- 192.168.1.20 ping statistics ---
=> 3 packets transmitted, 3 received, 0% packet loss, time 2954ms
=> rtt min/avg/max/mdev = 0.255/0.660/1.388/0.516 ms

I can even easily connect via port 80 (using Firefox on the laptop)
to this device, e.g., 
$ firefox http://192.168.1.20 

In fact, time and time (and time) again, everything works just fine, 
for about 2 to 5 minutes, until, invariably, I lose all connectivity!

What seems to happen is that CentOS wipes out my IP address that I 
had set for eth0. So, I lose all connectivity.

$ ifconfig eth0
=> eth0    Link encap:Ethernet  HWaddr A0:BE:C1:D8:E5:F1  
=>         inet6 addr: fe80::f2de:f1ff:fe38:8591/64 Scope:Link
=>         UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

I can repeat the process, and everything works again, for about 2 to
5 minutes. Then I lose my eth0 IP address again. 

WHAT I WANT:
When I set eth0 to an IP address, I want eth0 to *stay* at that IP address!

My question:
Q: Why does setting an eth0 IP address only last about 5 minutes on Centos?
What am I doing wrong?
What can I do to *keep* the IP address on eth0 that I set for eth0?